Former DNC Chair Donna Brazile is backing Vice President Kamala Harris in the 2024 election and predicted she would be the nominee, but left open the possibility of an open convention that would land her the nomination.

"Part A was Biden-Harris. Part B was Harris and her running mate. Part C would likely be an open convention” where Harris would likely prevail, Brazile, an ABC News contributor, told ABC News Live.

Harris has not yet said whether she will be running for president.

"She would be and is the strongest candidate," Brazile said.

After Biden's announcement that he would end his reelection campaign, Michigan Gov. Gretchen Whitmer praised him in a post on X.

"President Biden is a great public servant who knows better than anyone what it takes to defeat Donald Trump," she wrote. "His remarkable work to lower prescription drug costs, fix the damn roads, bring supply chains home, address climate change, and ensure America's global leadership over decades will go down in history."

"My job in this election will remain the same: doing everything I can to elect Democrats and stop Donald Trump, a convicted felon whose agenda of raising families' costs, banning abortion nationwide, and abusing the power of the White House to settle his own scores is completely wrong for Michigan," she wrote.

California Gov. Gavin Newsom -- one of Biden's top surrogates and is often floated as a potential replacement at the top of the ticket -- thanked the president for his leadership.

"President Biden has been an extraordinary, history-making president — a leader who has fought hard for working people and delivered astonishing results for all Americans. He will go down in history as one of the most impactful and selfless presidents. Thank you, @JoeBiden," Newsom said in a post on X Sunday.

First lady Jill Biden responded to her husband, President Joe Biden's decision to leave the presidential race on Sunday, reposting his announcement with a heart emoji.

Biden’s granddaughter, Naomi Biden, wrote in a post on X that she is "proud today of my Pop."

"I’m nothing but proud today of my Pop, our President, Joe Biden, who has served our country with every bit of his soul and with unmatched distinction," she wrote. "Not only has he been — and will continue to be — the most effective president of our lifetime, but he has likely already cemented himself as the most effective and impactful public servant in our nation’s history."

"He has been at the center of, and had a material impact on, literally every single major issue that our country and world has faced for 50 years," she added. "Our world is better today in so many ways thanks to him. To the Americans who have always had his back, keep the faith. He will always have ours."