President Biden and former President Donald J. Trump on Tuesday secured the delegates necessary to clinch their parties’ presidential nominations, according to The Associated Press, cementing a general election rematch in November months in the making.

Both men and their campaigns have long anticipated this moment. Mr. Biden faced only token opposition in the Democratic primary, as is typical for a sitting president, while Mr. Trump had been his party’s dominant front-runner for months.

Their November collision began to look even more likely after Mr. Trump scored a decisive win in Iowa in January. His victory cleared the field of all but one of his major Republican rivals and put him on a glide path to his party’s nomination. His last remaining primary challenger, Nikki Haley, suspended her campaign last week, further clearing a path that had already been remarkably free of obstacles for a candidate facing considerable legal problems.

The Associated Press named Mr. Biden the presumptive Democratic nominee on Tuesday after projecting his victory in Georgia, while Mr. Trump was designated the presumptive Republican nominee after he swept the G.O.P. contests in Georgia, Mississippi and Washington State. Later, Mr. Trump captured the Republican caucuses in Hawaii.

Tuesday’s results cleared the way for a 2024 general election campaign that, at just under eight months, is set to be one of the longest in modern American history and will be the country’s first presidential rematch in nearly 70 years.

Already, Mr. Trump and Mr. Biden had shifted their focus away from the primaries. With the president facing no significant challengers, Mr. Biden’s campaign speeches emphasized not just his record but the danger he believes is posed by Mr. Trump.