Real estate mogul Trump swept the GOP's five presidential primaries, extending his delegate lead over Sen. Ted Cruz of Texas and Ohio Gov. John Kasich. Former Secretary of State Clinton, meanwhile, won four of the five Democratic contests, adding to her advantage over Sen. Bernie Sanders of Vermont.
Those results made a Clinton-Trump general election contest more likely than ever, and both candidates acknowledged that their opponents' chances were dwindling. Those declarations came 86 days after the tumultuous primary-caucus season began in Iowa on Feb. 1.
"As far as I'm concerned, it's over," Trump said after his Tuesday night victories.
Trump still needs strong showings in upcoming contests, like next week's Indiana primary, to secure a majority of delegates before the party convention in July. But in the wake of victories he called "conclusive," Trump questioned why his rivals remained in the race.
Cruz and Kasich, who can no longer lock up the nomination through the primaries, are attempting to limit Trump's delegate gains and push an open convention in Cleveland. Trump, however, contended they have "no path to victory."
The New York businessman asked on Tuesday why Kasich was still in the race, and contended Cruz was "wasting his time" by considering vice presidential picks.
Cruz, for his part, called on supporters in the critical state of Indiana to unite around him as the primaries move away from the Northeast. "The media is going to say 'the race is over' ... But I've got good news for you. Tonight, this campaign moves back to favorable terrain," Cruz said.
On the Democratic side, Clinton sought to turn to the general election on Tuesday night.
"With your help we're going to come back to Philadelphia for the Democratic National Convention with the most votes, and the most pledged delegates," Clinton said during her victory speech.
"We will unify our party to win this election, and build an America where we can all rise together — an America where we lift each other up instead of tearing each other down," she said.
Clinton characterized her campaign as the ideal vehicle for achieving Democratic aims. Sanders has regularly described his candidacy as part of a revolution, but Clinton said: "We have to be both dreamers and doers" to achieve political progress.
"We're setting bold, progressive goals backed up by real plans," she said.
Still, the Democratic front-runner extended conciliatory words to Sanders and his voters.
"I applaud Senator Sanders and his millions of supporters for challenging us to get unaccountable money out of our politics and giving greater emphasis to closing the gap of inequality," she said. "And I know together we will get that done."
Trump on Tuesday urged Sanders to run as an independent should he lose the party's nomination. This would presumably sap votes from a Clinton ticket in the general election.
Clinton emphasized that her party should stick together.
"Because whether you support Senator Sanders or you support me, there's much more that unites us than divides us," Clinton said, pointing to Democrats' agreement that "wages are too low, and inequality is too high, that Wall Street can never again be allowed to threaten Main Street, and we should expand Social Security."
During her speech, Clinton repeatedly spoke of "we Democrats."
Although Sanders won Rhode Island on Tuesday, Clinton notched victories in Delaware and the comparatively delegate-heavy Maryland, Pennsylvania and Connecticut contests. Trump easily won all five of those states on the GOP side.
CORRECTION: This article was changed to reflect that Tuesday was 86 days after the Iowa caucus.