Election 2024 updates: Gov. Andy Beshear says JD Vance 'ain't from Appalachia' while campaigning for Harris

A person who has spent time with Biden and his family over the last couple of days told ABC News that "contrary to the reports I have heard there is no anger or remorse here."

"There is in only a deep sense of pride and an enormous amount of gratitude and appreciation for the overwhelming recognition of him as a true patriot and historic defender of democracy," the source said.

"I believe that it will be remembered as one of the most selfless acts done in the interests of the greater good in the history of American politics," they added.

-ABC News' Eric Avram

Biden's bombshell announcement was delivered in a letter to Americans posted on social media on Sunday as he recovered from COVID-19 at his residence in Rehoboth, Delaware.

The post on X came just one minute after he told staff of his decision, sources told ABC News.

"It has been the greatest honor of my life to serve as your President," Biden wrote. "And while it has been my intention to seek reelection, I believe it is in the best interest of my party and the country for me to stand down and to focus solely on fulfilling my duties as President for the remainder of my term."

Tonight's speech will be his first time discussing his decision at length and in front of the cameras to the nation.

About 500 White House staffers will be gathered together tonight to watch President Biden's remarks from the White House State Floor, which includes the East Room and State Dining Room.

Just before 7 p.m., there was a procession of staffers making their way over from the Eisenhower Executive Office Building, where most staffers work, to the White House North Portico entrance.

-ABC News' Karen Travers

Donald Trump is currently holding a rally in Charlotte, North Carolina -- his first since Biden dropped out of the race.

The former president quickly turned his focus to Harris, claiming she is "the ultra-liberal driving force behind every single Biden catastrophe."

"You know, I was supposed to be nice," Trump said. "They say something happened to me when I got shot, I became nice. And when you're dealing with these people, they're very dangerous people. When you're dealing with them, you can't be too nice. You really can't be. So, if you don't mind, I'm not going to be nice."