President Donald Trump said the alleged gunman had been killed. Federal law enforcement officials identified the alleged shooter as James Hodgkinson, 66, of Belleville, Illinois.
Five people, including Scalise, the third ranking member of House Republican leadership as the majority whip, were hospitalized.
Scalise was in critical condition after surgery, according to So Young Pak, spokeswoman for MedStar Washington Hospital Center. In a statement released at 8:15 p.m., the hospital said Scalise was struck by the bullet in his left hip. The bullet then traveled across his pelvis, fracturing bones and injuring internal organs, which caused severe bleeding. The hospital said he was in shock when he arrived.
Scalise underwent immediate surgery and an additional procedure to stop the bleeding, the hospital said. He remains in critical condition and will require additional surgeries. The hospital also said he has received multiple blood transfusions.
His wife Jennifer and their two young children were traveling up from New Orleans to Washington now to be with him.
Trump made an evening visit to the hospital. He arrived around 8:45 p.m. ET for the surprise visit and was accompanied by his wife, first lady Melania Trump. The couple brought flowers for the injured lawmaker.
A White House officials said Trump may only be able to visit with Scalise's family as the lawmaker remains in critical condition.
A congressional staffer, Zach Barth, was also shot in the leg and has since been released from the hospital. Matt Mika, a lobbyist for Tyson Foods and former staffer, was also identified as one of the victims. He was out of surgery and in critical condition as of Wednesday afternoon, according to a statement from his family.
House Speaker Paul Ryan also identified two members of the Capitol Police who were injured, Crystal Griner and David Bailey. In a statement, Capitol Police said Griner was in "good condition in the hospital having been shot in the ankle," and that Bailey "was treated and released having sustained a minor injury during the incident."
Rep. Roger Williams, a Texas Republican, was also hospitalized and released with an injury to his ankle.
As of Wednesday afternoon, Mika was in surgery and in critical condition, according to a statement from his family.
Lawmakers who were there described a chaotic scene, with many members of the congressional GOP baseball team huddled in a dugout while Capitol police who were part of Scalise's security detail and local Alexandria police engaged in a shoot-out with Hodgkinson. Congressional and law enforcement sources described it as a "deliberate attack."
WATCH: FBI UPDATES PUBLIC ON VIRGINIA SHOOTING
Traces are still being done on the two firearms recovered at the scene -- an SKS rifle 7.62 (which is a Chinese-made AK variant) and a 9 mm pistol, a law enforcement source tells CNN.
House Republican and Democratic leaders called for unity and praised the police, while Trump in an address from the White House said that the prayers of the nation and world are with Scalise.
"Congressman Scalise is a friend, and a very good friend," Trump said. "He's a patriot. And he's a fighter. He will recover from this assault -- and Steve, I want you to know that you have the prayers not only of the entire city behind you, but of an entire nation, and frankly the entire world. America is praying for you and America is praying for all of the victims of this terrible shooting."
Ryan condemned the shooting and praised the Capitol police on the House floor later Wednesday.
"We are united. We are united in our shock. We are united in our anguish. An attack on one of us is an attack on all of us," Ryan said, drawing a bipartisan standing ovation.
Members of Congress were practicing for a game that was scheduled for Thursday night at Nationals Park. Rep. Martha McSally, R-Arizona, said the game will still go on as scheduled. The annual game has been played since 1909, and McSally said lawmakers applauded the announcement at an all-members meeting.
Rep. Joe Barton, who manages the Republican team, said at a news conference that the game has added the Fallen Officers Fund as a charity it's sponsoring.
Rep. Mike Doyle, who manages the Democratic team, said at the same conference that they would like to host the entire Republican team at the Democratic club for dinner to reflect Wednesday night. "Some of them have probably never set foot in that building," he joked.
Representative Ruben J. Kihuen (D-NV) captured the Democrats' baseball team huddled in prayer after they found out about the shooting.
Lawmakers who spoke at the scene to reporters described a normal morning practice, at a field where they've practiced for years, when suddenly shots rang out. Lawmakers, staff members and even the young son of one of the members ran for cover, jumping into dugouts and over fences to avoid the gunshots.
WHAT WE KNOW ABOUT THE SHOOTER
Federal agents showed up at 66-year-old James T. Hodgkinson's home in Belleville, Ill., Wednesday. Around there they call him "Tommy" and his friends said Tommy never backed down from a fight.
"I just want to let people know that he wasn't evil, he was just tired of some of the politics that were going on," said Dale Walsh, childhood friend.
ATF agents searched the rural property belonging to Hodgkinsons, which his wife said he left in March when he packed up and headed to Northern Virginia. He had apparently been living in his car, and bartenders at a local barbeque restaurant near Alexandria which he frequented described him as creepy.
"I just remember him being extremely quiet. Didn't really make eye contact, and then would be staring when I was looking away," said Jamie Craig, bartender.
Hodgkinson was formerly a self-employed home inspector. He had been fired from contracting work within the town.
"He got loud, and she asked him to leave the office, at which point he did," said Mark Kern, former Belleville mayor. "At that point he was barred from doing business with St. Clair County"
Court records revealed a long and unsettling history of incidents with guns. In 2006, Hodgkinson was charged with battery and aggravated discharge of a firearm after he allegedly fired a shotgun during an argument and pointed it at someone's face. Those charges were eventually dismissed.
In March, neighbors called St. Clair County sheriff's deputies to Hodgkinson's home after they heard more than 50 shots fired in the woods, close to nearby homes. Deputies said he had a valid FOID card and wasn't breaking any laws.
"I yelled and I said, 'What the hell are you doing? Stop shooting, there's a house over there.' There were some more shots and evidently he didn't hear me or he didn't care," said neighbor William Schaumleffel.
Hodgkinson, who was photographed a Belleville protest, wrote a series of letters to his local paper and apparently volunteered for the Bernie Sanders campaign.
Hodgkinson's Facebook page is largely political, his profile picture is a caricature of Bernie Sanders as Uncle Sam.
The Facebook feed is filled with anti-Trump sentiments such as "Trump is guilty and should go to prison for treason."
He also "liked" a political cartoon that suggested Scalise should be fired. On March 22, he posted "Trump is a Traitor. Trump Has Destroyed Our Democracy. It's Time to Destroy Trump & Co."
"I didn't know anything about his Facebook page, all I'm saying is I knew him going through our years and it just took me by surprise, what he did," Walsh said.
Vermont Sen. Bernie Sanders said both in a statement and on the Senate floor that he had learned the shooter volunteered on his presidential campaign -- and that he condemned the shooting "in the strongest possible terms."
"I have just been informed that the alleged shooter at the Republican baseball practice is someone who apparently volunteered on my presidential campaign," Sanders said.
"I am sickened by this despicable act. Let me be as clear as I can be. Violence of any kind is unacceptable in our society and I condemn this action in the strongest possible terms," he said. "Real change can only come about through nonviolent action, and anything else runs against our most deeply held American values."
Staff members told ABC News they have yet to find someone who worked on the campaign that remembers him. He volunteered in Iowa. Staff members said his work appeared to be minimal and social media posts suggest he once hosted a debate watch party. Sanders' former Iowa state director said Hodgkinson was not on the campaign payroll and the state had more than 10,000 volunteers.
ILLINOIS CONGRESSMEN SHAKEN BY SHOOTING, CITE POLARIZATION IN POLITICS
Politicians from Illinois have been emotional about the shooting, and several were close with Scalise and other victims. Several also said it's time to tone down the divisive political rhetoric which has come from both parties and their supporters.
Rep. Rodney Davis (R-IL 13th District) was at the practice, but he was not hurt, his office said. Rep. John Shimkus (R-IL 15th District) was not at the practice, his office said.
"I was batting. We heard a loud noise. Felt like a construction site, somebody dropped a big piece of metal. And then the next thing I remember is somebody on the field yelling run, he's got a gun. I ran into the dugout, like most people on the field," Davis said.
He ran to the dugout on the first base side.
"Then eventually worked my way out of the dugout to other cover and disperse, and I got to witness the heroism of the Capitol Police that were there as part of Steve Scalise's detail. If they wouldn't have been there, this would have been a massacre of innocent people," Davis said.
Illinois Congressman Adam Kinzinger was not at the practice, but recently faced a death threat that resulted in the arrest of a suspect in Colorado.
"It's gotten to the point where most people can limit their hate and anger to a Facebook post, but as we all know there are people with mental illness who can take that to the next level and make the decision to turn violent," Kinzinger said.
Northwestern University political science professor Alvin Tillery said the political rhetoric seems to get amplified by social media. The suspect had a long history of angry social media postings.
"We are in a period of hyperpolarization, and this is problematic, but I do want to remind Americans that this is nowhere near the worst we have seen in our country," Tillery said.
Tillery pointed out that during the 1890s, Reconstruction, there were political lynchings and assassinations. It was also pretty violent during the 1960s. In that decade, both President John F. Kennedy and U.S. Attorney General/presidential candidate Robert Kennedy were assassinated.
WITNESSES DESCRIBE SCENE DURING MASS SHOOTING
Members described Scalise dragging himself roughly 15 yards away from second base, where he had been playing, and lying there until the shooter was neutralized, at which point some of them ran to assist him and apply pressure to the wound until he could be evacuated. Once they were able, Sen. Jeff Flake said he and Rep. Brad Wenstrup, who is a physician, went to where Scalise was lying to apply pressure to the wound. Scalise was coherent the whole time, Flake said.
Kentucky Sen. Rand Paul told CNN "it would have been a massacre" without the Capitol Hill Police officers present.
"Nobody would have survived without the Capitol Hill police," Paul said on CNN. "It would have been a massacre without them."
"We had nothing but baseball bats to fight back against a rifle with," Alabama Rep. Mo Brooks said.
Flake added that he saw a member of Scalise's security detail return fire on the gunman for what felt like 10 minutes, even though the police officer was wounded in the leg.
"Fifty (shots) would be an understatement, I'm quite sure," Flake said when asked about the total amount of gunfire, including police returning fire.
Brooks said the shooter was behind the third base dugout and didn't say anything.
"The gun was a semiautomatic," Brooks said, adding that he was sure it was a rifle but unsure what kind. "It continued to fire at different people. You can imagine, all the people on the field scatter."
CAPITOL HILL INCREASES SECURITY, CANCELS EVENTS
The news of the shooting reverberated on Capitol Hill, where security was increased and regular proceedings were canceled or postponed.
He also said he'd seen an image of members of the Democratic congressional baseball team huddled in prayer after learning of the shooting.
"Every day we come here to test and to challenge each other. We feel so deeply about the things that we fight for and the things that we believe in. At times, our emotions can clearly get the best of us. We are all imperfect. But we do not shed our humanity when we enter this chamber. For all the noise and all the fury, we are one family," Ryan said.
The House decided to not hold any votes on legislation Wednesday, and many hearings were delayed. The House Natural Resources Federal Lands Subcommittee also canceled a scheduled meeting to debate gun legislation.
Capitol Hill Police notified congressional offices that the security presence on the Hill would be increased "out of an abundance of caution."
POLITCIANS REACT TO VIRGINIA SHOOTING
"I am shocked and horrified by the events that took place this morning. My thoughts and prayers are with Rep. Steve Scalise, the U.S. Capitol Police, the Congressional staffers present at this morning's practice, and all those affected. I wish everyone injured a full and speedy recovery," Rep. Jan Schakowsky (D-IL 9th District), Chief Deputy Whip, said in a statement released Wednesday.
"As we continue to learn more about what happened this morning, we know that it could have been much worse if it wasn't for the swift action by our U.S. Capitol Police and the first responders of Alexandria, Va. My thoughts and prayers are with my friend Steve Scalise, our Capitol Police special agents, our staff and aides, and all of their families. I extend my best wishes to each of them for a safe and speedy recovery. What happened today was a targeted act of senseless violence from a disturbed individual. This hate will not divide us; it will unite us. Today and every day, I am grateful to our Capitol Police and our strong Congressional community," Rep. Adam Kinzinger (R-IL 16th District) said in a statement released Wednesday.
"My thoughts and prayers are with Whip Steve Scalise, the Congressional Staff and Capitol Police all affected by this morning's horrible shooting. We are grateful for the heroism of the Capitol Police who saved countless lives. We are united in our hopes and prayers for the wounded," Rep. Bobby Rush (D-IL 1st District) said in a statement released Wednesday.
"I am deeply saddened by the shooting this morning in Alexandria, Virginia. Elizabeth and I are praying for Rep. Steve Scalise, the Capitol Police, and all those involved. I wish those harmed a speedy recovery and commend the bravery demonstrated by the Capitol Police and those who tended to the injured. We are fortunate to live among the brave men and women in uniform who serve to keep us safe each and every day," Rep. Peter Roskam (R-IL 6th District) said in a statement released Wednesday.
"We're praying together now in Capitol for colleagues, staff, Capitol Police, families & all affected by senseless shooting. Please join us," Rep. Randy Hultgren (R-IL 14th District) said in a statement released Wednesday.
"This is a sad day for all Americans, regardless of political affiliation. We can all agree that these sorts of actions simply have no place in civil society, and we should do much more to prevent this sort of needless violence. I wish all the victims a speedy recovery and look forward to seeing my former House colleagues, Congressional staffers and Capitol Police officers back on the Hill soon. I also want to thank all the first responders for their bravery in risking their lives this morning-without their efforts, today could have been even worse," Sen. Tammy Duckworth (D-IL) said in a statement released Wednesday.
"My thoughts are with Majority Whip Steven Scalise and my colleagues, their staffers, families, and the Capitol Police who work hard to keep Members of Congress safe. This kind of cowardly attack on Members of Congress is horrific. Violence has no place in our government or politics, and I wish everyone who was injured a speedy recovery," Rep. Bill Foster (D-IL 11th District) said in a statement released Wednesday.
Cook County Commissioner Richard Boykin released this statement Wednesday morning on the need to refocus on preventing gun violence:
"The tragic shooting in Virginia this morning underscores the importance of implementing policies to fight gun violence. From the streets of Chicago to a baseball field in Virginia, all people deserve to be safe. The attack this morning also underscores the unsavory political discourse in our country. It is lunacy that an individual was so enraged over political differences that he would take up arms and attack sitting congressmen and their staffs. I offer best wishes for Rep. Steve Scalise and everyone impacted by the attack this morning. I also send condolences to the family of the accused shooter, because today is a tragic one for them as well. As a nation, we must pull together and allow the truest form of our humanity to shine brightly. This tragedy must bring us closer together."
Scalise is the first member of Congress to be shot since former Arizona Rep. Gabby Giffords in January 2011. Giffords was shot in the head by Jared Lee Loughner at a "Congress On Your Corner" event at a Tucson grocery store. Giffords, who authorities said was the main target of the shooting, survived the attack but six others were killed and an additional 12 were injured.
Loughner pleaded guilty in 2012 and was sentenced to life in prison without the possibility of parole.
WLS-TV contributed to this report.
(The-CNN-Wire & 2017 Cable News Network, Inc., a Time Warner Company. All rights reserved.)