Vice President Kamala Harris' husband, second gentleman Doug Emhoff, commented for the first time Sunday night since President Joe Biden announced his decision to drop out of the 2024 race.

"President Biden is a true patriot who leads our nation with honesty, decency, and integrity," Emhoff wrote in a post on X.

Praising Biden's work with Harris, Emhoff said, "They have fought tirelessly for families and communities, delivering for Americans across our nation."

"I am so proud of their accomplishments and thankful for their leadership," he added.

After President Joe Biden ended his bid for reelection and endorsed Vice President Kamala Harris Sunday, many have begun to wonder how the remainder of the 2024 race will unfold -- including the upcoming presidential debate in September, hosted by ABC News.

Michael Whatley, Republican National Committee chairperson, told ABC News' David Muir that the former president has said "he would accept a debate anywhere, anytime, anyplace."

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Would Donald Trump and Kamala Harris debate?

Now that Biden is out of the race, Chairperson of the RNC Michael Whatley says they still welcome a second debate with "Kamala Harris or anybody else."

Whatley said Trump would have to make the official confirmation of the debate, however, he said, "We've made it very clear that we welcome that debate."

"We want to talk about the contrast between the Biden-Harris agenda and Donald Trump's agenda where he is going to unite America and lead us into a bolder future," Whatley said.

Former New Jersey Gov. Chris Christie told ABC News' David Muir Sunday night that Kamala Harris' entry into the presidential race will have a big impact.

"Look, this absolutely changes the race, David. I think anybody who says this doesn't change the race doesn't understand politics," Christie said. "But here's the big question, 'How does it change the race?' And none of us know that [answer] yet. And the reason we don't is because that's going to depend almost exclusively on the performance of these two candidates now."

Christie, who ran for the 2024 GOP nomination for president but dropped out during the primaries, said running for president is different than campaigning for vice president.

"[S]he's going to be under a different level of scrutiny, a different level of pressure, and there's a different expectation level for her than there has been before," Christie said. "So how does she perform, and how does Donald Trump change his approach? He's now not running against 81-year-old Joe Biden. He's running against a much younger woman. And that's going to change the dynamic, too."

Christie said Trump will need to change his tone with Harris coming to the fore.

"Look, when I ran the first time for governor, David, I ran against an incumbent, democratic male. When I ran for reelection, I ran against a woman. And the pace of that race and the way you conduct yourself as a male candidate [against] the female candidate has to have a bit of a different tone to it," Christie said. "The question for me is going to be, 'Can Donald Trump adjust to that, and how will he react to this new dynamic? So, we're to see some very interesting developments over the course of the next number of weeks."

-ABC News’ Jolie Lash

Sen. Elizabeth Warren, D-Mass., released a video testimonial on X Sunday explaining why she's backing Vice President Kamala Harris as the new Democratic nominee.

"She is ready to step up, bring our party together, go toe to toe with Donald Trump and win in November," Warren said in the video, in which she speaks directly to the camera.

"Kamala has been a ferocious warrior on the issue of abortion and under Kamala's leadership we are going to get Roe V. Wade back into the law of the land," Warren said.

"When you're up against a convicted felon who better than a former prosecutor to take it straight to Donald Trump," she continued. "I'm here for Kamala because Kamala has been here for the American people year after year after year."

-ABC News' Allison Pecorin