Former Republican Rep. Adam Kinzinger endorses Biden, whose campaign wants to flip anti-Trump GOP

CHICAGO -- Republican former congressman Adam Kinzinger endorsed President Joe Biden on Wednesday, giving the Democrat a prominent new ally in his high-stakes campaign to win over moderate Republicans and independents this fall.

Kinzinger, a military pilot who emerged as a fierce critic of former President Donald Trump after the U.S. Capitol was attacked by Trump's supporters, described Trump as "a direct threat to every fundamental American value" in a video announcing the Biden endorsement.

ABC7 Chicago is now streaming 24/7. Click here to watch

"While I certainly don't agree with President Biden on everything, and I never thought I'd be endorsing a Democrat for president, I know that he will always protect the very thing that makes America the best country in the world: our democracy," said Kinzinger, who voted for Trump in 2020.

The former Illinois congressman also issued an ominous warning. Trump, he said, will "hurt anyone or anything in pursuit of power."

Kinzinger's announcement comes on the eve of the opening presidential debate and gives Biden an example he can raise Thursday night of a well-known Republican supporting him over Trump. Biden's camp is prioritizing outreach to moderate Republicans and independents alienated by Trump's tumultuous White House tenure.

Kinzinger becomes the highest-profile Republican official formally backing Biden, whose campaign earlier in the month tapped Kinzinger's former chief of staff Austin Weatherford to serve as its national Republican outreach director. Republican former Georgia Lt. Gov. Geoff Duncan also endorsed Biden last month.

Ultimately, a number of prominent Republicans are expected to join Biden's campaign, with more influential names likely to be announced closer to the November election.

Shortly after Kinzinger announced his decision, Biden shared the endorsement video on social media and said he was grateful for the Republican's support.

"This is what putting your country before your party looks like," Biden wrote on X.

SEE ALSO: 5 things to watch in the first 2024 general election debate

Biden's team is trying to create what it calls "a permission structure" for Republican voters who would otherwise have a difficult time casting a ballot for the Democratic president.

Kinzinger developed a national profile as one of two Republicans who served on the House's committee investigating the Jan. 6, 2021, attack. The committee highlighted a number of Trump's transgressions before and during the deadly attack on the U.S. Capitol as Congress tried to certify the election results for Biden.

Kinzinger, who did not seek reelection in 2022 after voting to impeach Trump for his role in the Jan. 6 attack, called on the GOP to change course.

"To every American of every political party and those of none, I say now is not the time to watch quietly as Donald Trump threatens the future of America," said Kinzinger, who repeatedly described himself as a conservative in the video. "Now is the time to unite behind Joe Biden and show Donald Trump off the stage once and for all."

In a statement Wednesday, Biden campaign manager Julie Chavez Rodriguez described Kinzinger as "a true public servant who is a model for putting our country and our democracy over party and blind acquiescence to Trump."

"Congressman Kinzinger represents the countless Americans that Donald Trump's Republican Party have left behind," she said. "Those Americans have a home in President Biden's coalition, and our campaign knows that we need to show up and earn their support."

Trump and his allies have long dismissed Kinzinger's efforts to rally Republicans against him. The former president publicly celebrated when Kinzinger didn't seek reelection and has called for the prosecution of Kinzinger and others who served on the Jan. 6 committee, part of his pattern of suggesting his opponents face government retribution.

Biden has been particularly focused on courting supporters of Republican former presidential candidate Nikki Haley, who continued to win over a significant number of anti-Trump GOP primary voters throughout the spring even after suspending her campaign.

As part of Biden's sustained outreach to moderate voters in both parties, his campaign released an ad highlighting Trump's often-personal attacks against Haley, including his primary nickname of her as "birdbrain" and suggestion that "she's not presidential timber."

Haley last month said she will vote for Trump in the general election.

Biden is also targeting so-called hold-your-nose Trump supporters.

"They liked the independence of Donald Trump. They liked being a patriot, but they don't like Donald Trump because, for other personal reasons, this might help that group. That's a little group, but, in this election, every little bit is going to be important," political consultant Thom Serafin said.

Indeed, Trump's grip on his party's passionate base is stronger than ever. And the overwhelming majority of Republican elected officials are backing his 2024 campaign, even those few, like Haley, who worked against him in the primary phase of the campaign.

Kinzinger now works as a political commentator.

This early in the election cycle, it's not clear how impactful Kinzinger's endorsement will be, but political observers say it's no coincidence that it's coming out on the eve of the first presidential debate.

"We are expecting President Biden to go really hard against President Trump on Jan. 6, upholding democracy and those things that he's been doing the last four years. And so that current corresponds very well with what Adam Kinzinger said in his endorsement today," said Suzanne Chod, a North Central College political science professor. "How Biden uses him and where he might go, we'll see whether there'll be any real effect."

Newly elected Illinois Republican National committeewoman Rhonda Belford was quick to dismiss Kinzinger's statement Wednesday.

"Well, you know, he's trying to be relevant, of course, and just trying to stand out. It's pretty much a joke from our standards," Belford said.

On Wednesday, Kinzinger said the reason behind his endorsement is very simple.

"What is so important about this election, even beyond who's fighting for themselves and who's fighting for the country, and the reality is because there is a fight for democracy, that if we don't buckle down and take seriously, we could lose that fight for democracy," he said.

Kinzinger said he has not had any discussions with the Biden campaign, but would be willing to do whatever he can to help Biden get reelected.

ABC7 Chicago's Craig Wall contributed to this report.