Biden’s Goodbye to Politics Will Begin in Earnest With His Convention Speech

President Biden’s goodbye to a half century in national politics will begin in earnest on Monday.

When he takes the stage at the Democratic National Convention in Chicago that evening, Mr. Biden will establish his time in office and his political legacy as the foundation for the candidacy of Vice President Kamala Harris, the new Democratic nominee.

According to Biden aides who previewed the themes of the president’s remarks, he will say that she is the best person to finish a campaign he started — one that remains rooted in protecting democratic ideals and preventing a second term for former President Donald J. Trump, the Republican nominee. The aides spoke on condition of anonymity because they were not authorized to detail the plans.

It will be a bittersweet moment for Mr. Biden, who left the race and turned the keys of his campaign over to Ms. Harris less than a month ago. Since then, she has headlined packed rallies and delivered forceful campaign speeches, and the president has largely receded from center stage.

But Mr. Biden, who is supportive of Ms. Harris and appreciates the momentum around her, the aides said, plans to ramp up his campaign schedule. He has also been focused on sealing up his legacy as a one-term president — but one who pulled the nation out of an economic spiral during the coronavirus pandemic, a point he will make in his speech.

On Friday, Mr. Biden left Washington for Camp David for the weekend; he was scheduled to workshop his speech with Mike Donilon, a close adviser, and Vinay Reddy, his chief speechwriter.

In his speech, the president will also frame Ms. Harris’s campaign as continuing policies and ideals he has long championed. Mr. Biden’s remarks will make the case that “democracy prevailed” with his election in 2020. A win for Ms. Harris and her running mate, Gov. Tim Walz of Minnesota, in November will mean that “democracy is preserved.”