The broad support for Mr. Trump spanned some of the dividing lines that have characterized the Republican race until now: He won among the affluent and college-educated as well as with blue-collar voters and those with no more than a high school education, according to exit polls.

But the unease about Mr. Trump’s candidacy in some quarters of the party persisted, a potential warning sign if he emerges as the nominee. About a quarter of Republican primary voters in Connecticut, Maryland and Pennsylvania said they would not support him if he were the party’s nominee. The resistance to Mr. Trump was greatest among Mr. Kasich’s supporters, who are more moderate-leaning: Six in 10 said they would not vote for Mr. Trump in November.

Mrs. Clinton was lifted once again by strong backing from blacks and older voters, but she also ran stronger with white voters than she has in many states. In Pennsylvania, she narrowly won among whites. Her performance was even better in Maryland, where she carried white voters by 12 points.

Mr. Trump’s advantage across all five states was so forbidding that Mr. Cruz abandoned the Northeast entirely on Saturday, and Mr. Kasich was left to pick up stray delegates. Mrs. Clinton and Mr. Sanders campaigned aggressively in Pennsylvania and Connecticut, but they focused largely on policy issues like fracking, gun control and Wall Street reform rather than sniping at each other as they did in a raucous televised debate in Brooklyn.

Not only did Mr. Trump have significant prospects for a substantial delegate haul Tuesday, a week after his dominating performance in New York, he also had the opportunity to send a clear message to party leaders and other Republicans that resistance to his nomination is futile.