President Biden will deliver a commencement speech to the graduates of Morehouse College on Sunday, an appearance that will put him directly in front of 500-plus young men who represent a slice of the electorate that is drifting away from him and toward his challenger, former President Donald J. Trump.

The commencement address at an all-male, historically Black college in Georgia, a state Mr. Biden flipped by a narrow margin four years ago, will give the president a chance to draw a character comparison between himself and Mr. Trump, as he does often, by using themes of freedom and democracy to illustrate what he believes is at stake in November.

On Saturday, Mr. Biden gave a preview of sorts to a group of supporters, many of them Morehouse alumni, shortly after his arrival in Atlanta. He told them that the election was not about two candidates but about a choice between protecting democracy and letting its ideals continue to backslide.

“It’s not about me. It’s about the alternative as well,” Mr. Biden said to the audience at Mary Mac’s Tea Room, a local business owned by a Morehouse alumnus. “My opponent’s not a good loser, but he is a loser. Our democracy’s really on the line.”

At a campaign reception shortly after, Mr. Biden warned that Mr. Trump represented an “unhinged” threat to the future of the country. “We cannot let this man become president,” he added. “We have to win this race, not for me but for America.”

After addressing Morehouse, Mr. Biden will travel to Detroit to speak at a dinner hosted by the N.A.A.C.P. A Sunday schedule that includes Air Force One hitting two battleground states in eight hours is the clearest sign yet that Mr. Biden is serious about reintroducing himself to voters who carried him to the White House in 2020 and whose support he will need to win again to stay in office.