Donald Trump and Hillary Clinton extended their leads in the Republican and Democratic presidential races in a string of East Coast primary wins on Tuesday, including in Pennsylvania, the day's biggest prize.

CNN declared Trump the winner in Pennsylvania within minutes of polls closing at 8 p.m. He later went on to win Maryland, Connecticut, Rhode Island and Delaware.

Meanwhile, Clinton took Maryland, Connecticut, Delaware and Pennsylvania, expanding her lead over U.S. Senator Bernie Sanders of Vermont, who only captured Rhode Island, in Tuesday's contests.

But despite the decisive victories, it’s unclear Tuesday’s election delivered the knockout punch Trump or Clinton were seeking in taking out their rivals: Republican Texas Senator Ted Cruz and Ohio Governor John Kasich, and Sanders.

The former secretary of state has an almost insurmountable lead of 275 pledged delegates heading into Tuesday's contests, and Senate Democratic leader Harry Reid told reporters he did not think Sanders had a realistic path to winning the nomination.

Reid said Sanders had run a "unique and powerful" campaign and he refused to urge him to step aside. But asked if he thought Sanders had a path to the nomination, he said: "No I do not."

A senior strategist for Sanders, Tad Devine, told the New York Times that Sanders would "reassess" any possible adjustments to his campaign after Tuesday, although he said the candidate would stay in the race.

For Trump, the Pennsylvania win, in particular, doesn't come without some complications, especially if the blustery New York businessman fails to get the 1,237 delegates needed to clinch the party's nomination and the Republicans have to hold a contested convention.

Seventeen of the 71 Republican delegates up for grabs in Pennsylvania on Tuesday are allocated to the candidate who wins its primary. The other 54 delegates - who are elected directly by voters - are free agents, able to support anyone they choose at the Republican National Convention in July. Some have indicated they will decide who to vote for during the convention.

The state features the sort of complex rules that Trump has repeatedly slammed for being "rigged" and that forced him this month to reshuffle his team to better compete with Ted Cruz.

Before polls opened, Trump kept battering the Republican delegate allocation system. "The whole delegate system is a sham," he said on Fox News.

Cruz and Kasich have formed an anti-Trump alliance in an effort to stop Trump from reaching a first-ballot victory at the convention in Cleveland, Ohio.

Former Republican presidential candidate Ben Carson, a Trump supporter, said the deal between Kasich and Cruz would backfire because it smacked of backroom politics.

"The people have sort of risen up and they’ve said we don’t want all this stuff that is going on, all this intricate, backroom stuff," Carson said on Fox News.

But Gertrude Taylor, 86, who was voting in the Philadelphia neighborhood of Fishtown, said she cast a ballot for Kasich because he was a "down-to-earth man" and there was "no way" she could back Trump.

"He's too outspoken, he gets mad if things don’t go his way. I think he should keep his thoughts to himself," Taylor said.

On Twitter, Trump expressed sympathy for Sanders, saying he had been "treated terribly" in the Democratic race. Clinton has added to her lead over Sanders with strong support from superdelegates free to back any candidate.

Trump, who would benefit if he faced two opponents in November instead of one, suggested Sanders "should show them, and run as an independent!" Sanders has said he would not make an independent run for the White House.

While railing against the Republican system, Trump announced on April 7 he was reorganizing his campaign to focus on delegate and convention strategy, hiring advisers with convention experience.

In Pennsylvania, candidates hope to get as many die-hard supporters as possible elected as delegates, both to build support on the first ballot and to bolster their position if no one gets to 1,237 delegates outright and the Cleveland convention becomes a protracted fight for the nomination.

It is unclear if Trump's campaign revved up its efforts in time to make a difference in Pennsylvania's delegate race.

U.S. Representative Lou Barletta of Pennsylvania, a Trump surrogate, said the campaign had taken some steps, including printing cards naming its preferred candidates for delegates so that voters going to the polls would know who backs Trump.

Before that, "we were just scribbling names on a piece of paper for them," Barletta said. "I think the organization coming here to Pennsylvania was just in the nick of time."

Cruz's Pennsylvania chairman, Lowman Henry, said he had not noticed a ramp-up by Trump there. "All we've noticed is a bunch of whining about it," he said. "Our response is: They whine, we win."

Cruz has met with would-be delegates who have promised to support him if they are elected, as well as candidates who have not declared any allegiance, Henry said. Kasich has also met with prospective delegates.

It is difficult to predict which presidential candidate will get the most support from Pennsylvania. Many delegate candidates have said they will vote for whoever wins the state or their district, at least on the first ballot at the convention.

If those delegates hold to their informal promises, Trump could win most of Pennsylvania's votes on the first round in Cleveland, said Charles Gerow, a conservative strategist also running to be a Pennsylvania delegate.

But if Trump falls short of the votes needed to win on the first ballot in Cleveland, and delegates across the country begin switching sides, the efforts now being made to woo Pennsylvania delegates could pay off.