President Biden clinched the Democratic nomination on Tuesday, securing enough delegates to send him into a looming rematch against former President Donald J. Trump after a mostly uncontested primary campaign that was nevertheless marked by doubts — even from supporters — over his age, foreign policy and enduring strength as a candidate.
Mr. Biden faced little opposition in his march to the nomination. Robert F. Kennedy Jr., the political scion and environmental lawyer, dropped out of the Democratic nominating contest to run as an independent. Representative Dean Phillips of Minnesota and the self-help guru Marianne Williamson never attracted more than a fraction of the vote.
In fact, Mr. Biden’s most serious rival was not a candidate but a protest movement over his support for Israel in its war in Gaza. The movement — organized by Muslim American activists and progressives — urged voters to cast their ballot for the “uncommitted” option rather than Mr. Biden.
It received significant support in Michigan, winning more than 101,000 votes, as well as in Minnesota and Hawaii. Organizers also targeted Washington State, which held its primary on Tuesday, although the full results there will not be known for several days.
Still, with his victory in Georgia, Mr. Biden on Tuesday crossed the necessary threshold of 1,968 delegates to become his party’s standard-bearer this year.
In a statement, Mr. Biden said he was honored that Democratic voters “have put their faith in me once again to lead our party — and our country — in a moment when the threat Trump poses is greater than ever.”
He looked toward November, saying, “Voters now have a choice to make about the future of this country. Are we going to stand up and defend our democracy or let others tear it down? Will we restore the right to choose and protect our freedoms or let extremists take them away?”
He added, “I believe that the American people will choose to keep us moving into the future.”
On the Republican side, Mr. Trump was expected to secure the Republican nomination later on Tuesday. The early conclusion to the nominating contests means Americans will face a lengthy general-election campaign. Mr. Trump, who faces 91 criminal charges in four cases, is leading Mr. Biden in many polls.
Voters have questioned Mr. Biden’s age and his record during his first term, even as economic indicators improve. The president has shown weakness with young people and Black and Hispanic voters, key groups in the coalition that powered him to victory in 2020. Only 83 percent of voters who backed him four years ago say they plan to do so again, according to a recent New York Times/Siena College poll. For Mr. Trump, the figure is 97 percent.
Mr. Biden is viewed unfavorably by a majority of Americans — a precarious position for a president seeking re-election — although so is Mr. Trump.
Mr. Biden and his allied groups do have a significant financial advantage over Mr. Trump, whose legal bills are taking a toll.
The Biden campaign has argued that Democratic voters will come back to the president as the choice crystallizes between him and Mr. Trump, whom Mr. Biden has portrayed as a threat to democracy.
Trying to assuage concerns about his age and stamina, Mr. Biden delivered a robust State of the Union address last week, followed by trips to crucial battleground states. He has also talked more forcefully about his accomplishments and begun to lay out his vision for a second term, and his campaign has started a $30 million advertising blitz.
The candidates will not be formally anointed as their parties’ nominees until their national conventions this summer. Democrats will hold their convention in Chicago starting on Aug. 19. Republicans will hold theirs in Milwaukee starting on July 15.
