The stakes were very high, and on Tuesday night, many people told ABC7 this debate delivered.
A large group of Democrats gathered for a debate watch party at the IBEW Hall at 22nd and Martin Luther King Drive.
At times, they applauded, booed and even groaned. It was a lively night, and some of those folks weighed in on the outcome.
"I think she did a great job of highlighting just the truth of who Donald Trump is and, most importantly, how dangerous he is," Illinois Comptroller Susana Mendoza said of Harris.
"I see this in her, this energy, and the same kind of energy is in this room, right, that we are going forward, that that's old news," said Democratic voter Regan Burke.
"She's again countering the lies that Donald Trump has told about the economy. He is not telling the truth about what he did with our economy," said Illinois. Lt. Gov. Juliana Stratton.
Elsewhere, the Chicago Republican Party hosted a pair of debate gatherings, including one on the Near West Side.
"He's projecting strength. He's showing America what we need," said Chicago Republican Party Chairman Chuck Hernandez.
There was a lot of energy in those rooms with animated reactions, and afterward, some strong opinions.
"The vice president has had a history of where we are now and the problems of the last four years, and she cant run away from those. And the president has addressed those issues," said Cook County State's Attorney candidate Bob Fioretti.
"I have to give Donald trump credit. He is a blunt instrument. He came in there and just tried to hammer some of his positions," said Illinois Republican Party Co-chair Aaron Del Mar.
At some of the gatherings, the parties built their organizations, getting people signed up for various campaign activities and capitalizing on the energy of debate night.
Earlier Tuesday, Illinois politicians from both parties weighed in on what the candidates needed to say to win over undecided voters.
How can Harris, Trump win over undecided voters during the debate?
"I think Kamala Harris is capable of managing through, but it's not easy. This guy is an actor, entertainer and a liar," said Gov. JB Pritzker.
Pritzker said Harris had the tall order of articulating her plan while managing expected falsehoods coming from Trump. From his own debate experience, the governor said, it is difficult to debate and fact check at the same time.
"Every time something comes up, do you counter what they are saying and point out what a lie it is? Or, do you use your short minute or two minutes to talk about what your plans are?" Pritzker said.
While the former president is not a traditional debater, Pritzker called Trump a great debater, because he wins by disrupting, but Trump supporters feared that strategy would not win over undecided voters.
"I think he needs or stay on topic, stay on-message and stay incredibly disciplined. I think it's going to be the biggest challenge for him tonight," Del Mar said.
Both candidates must win about 7% of the electorate who are undecided in a handful of swing states.
Former Illinois House Minority Leader Jim Durkin is a moderate Republican who is not supporting Trump, but he said Harris had to give meat on the bone Tuesday night to get independent voters on her side.
"They are not going to put somebody in who they who's not going to be able to put out a good plan about how they're going to be able to manage this job and how they're going to what their vision is for the United States," Durkin said.
Read Pritzker's full statement:
"Tonight, Vice President Kamala Harris showed the country exactly why she will be elected the next President of the United States.
"Kamala Harris is a proven leader who built her career standing up for America's working families. From strengthening the middle class to protecting individual rights and freedoms, she has repeatedly shown she has the character and vision to not just lead our country but to strengthen it. That character was on full display as she eviscerated Donald Trump, meeting his lies with truth, fear with optimism, and nonsense with real policies to help the American people.
"Donald Trump is a racist, misogynist, homophobe and 34-time convicted felon who can not be allowed to serve a second term. He is a pathological liar who flailed through tonight's debate legitimizing conspiracy theories instead of telling the American people what he would do for their families. A second Trump term would be spent further eroding Americans' rights and freedoms, gutting our middle class, and erasing the progress we've fought so hard to make. Donald Trump's answers tonight may have been a rambling mess but his end goal is not - Trump is in this race only to benefit himself and his allies, and he will use every lever of government to do so.
"The American people deserve better than the disgrace that is Donald Trump. They deserve a true champion for working families. They deserve Kamala Harris."
Read the Illinois Republican Party's full statement:
"Tonight, Americans saw a stark contrast between President Trump, a strong leader who outlined his vision to secure our border, lower prices and save our country, and Kamala Harris, who continued to lie about her record and socialist policy positions. President Trump is the leader that Illinois, and America needs and we continue to share our common sense solutions to turn Illinois around."
ABC7 Chicago Political Analyst Laura Washington broke down the key takeaways of Harris-Trump debate.
Political analyst breaks down Harris-Trump debate