Former Rep. Adam Kinzinger is in a unique position as a Republican: On Thursday, he is set to deliver a prime-time speech on the final day of the Democratic National Convention, speaking in support of Vice President Kamala Harris before she accepts her party's nomination for president.

Kinzinger, who retired from the House in 2023, has been a vocal critic of former President Donald Trump over the years, and although he describes himself as a "proud conservative," he endorsed then-candidate Joe Biden for reelection in June.

"Donald Trump poses a direct threat to every fundamental American value," Kinzinger said in his Biden endorsement video, mentioning Trump's role in the attack on the U.S. Capitol on Jan. 6.

The former Illinois congressman sat on the House's Jan. 6 select committee that investigated the attack. He was also one of the 10 House Republicans who voted to impeach Trump on a charge of inciting the Jan. 6 attack.

"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," Kinzinger said in support of the Democratic ticket.

Since Harris replaced Biden as the Democratic nominee, Kinzinger has supported the vice president, saying she stands for democracy.

"Donald Trump is a clear threat to the future of democracy, the future faith of democracy, and Kamala Harris has made it clear that she supports it even when we disagree on things," he said on CNN earlier this month.

Kinzinger's speech will round out a slate of Republicans who have spoken at the DNC this week, including former Georgia Lt. Gov. Geoff Duncan, Mayor John Giles of Mesa, Arizona, former Trump White House national security official Olivia Troye and former Trump White House press secretary Stephania Grisham.

In what's expected to be a close contest between Harris and Trump in November, the Harris campaign is leaving no stone unturned, targeting Republicans and independents in their messaging and outreach.

GOP speakers at the DNC appear to be doing the same.

"The sometimes awkward alliance between the left, center, and sane right will prevail! We're not going back," Kinzinger posted to X on Wednesday.