It’s dubbed the “Acela” primary and it could give Donald Trump and Hillary Clinton a major boost in their quest for their parties’ presidential nominations.

Voters in five states — Rhode Island, Connecticut, Pennsylvania, Maryland and Delaware — head to the polls Tuesday.

The contests have been nicknamed after the Amtrak express train that travels the Northeast Corridor from Washington to Boston. And if the polls are correct, challengers face stiff odds in their efforts to derail Trump and Clinton.

Trump needs another big night — like his win in New York last week — to stay on track toward winning enough delegates through primaries to avoid a contested GOP convention this summer. His opponents, Sen. Ted Cruz (R-Tex.) and Ohio Gov. John Kasich, hope to take a few delegates but largely have begun focusing on upcoming contests.

The Republican wild card Tuesday is Pennsylvania, where voters will elect 54 delegates who aren’t bound to any one candidate.

For Clinton, the contests offer another opportunity to push farther ahead of Sen. Bernie Sanders of Vermont.

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Clinton has a 721-delegate lead.

Further, four of the five states holding primaries are “closed” primaries, meaning only enrolled Democrats can vote, as in New York. That could be critical as Sanders has fared much better in “open” contests in which he received strong support from independents.

But Sanders isn’t conceding. His staff said Sanders has “pledged to carry his campaign through to Oregon, California” and the remaining states with upcoming primaries.

“From coast to coast, people are standing up. They are fighting back and they are saying that we need a government that works for all of us, not just wealthy campaign contributors,” Sanders said in Pittsburgh Monday.

Clinton, in contrast, continued an approach she began after her New York victory: Looking past Sanders and focusing on potential Republican rivals. In Delaware on Monday, she took aim at Trump.

“Come out of those towers named after yourself and actually talk and listen to people,” Clinton said in Wilmington. “Don’t just fly that big jet in and land it and go make a big speech and insult everybody you can think of and then go back in on that big jet and go back to your country club house in Florida or your penthouse in New York.”

For Democrats, 462 delegates are up for grabs Tuesday. Pennsylvania, with 210, and Maryland, with 118, are the biggest prizes. Clinton enjoys double-digit leads in polls in both states.

Trump also is expected to fare well in the “Acela” primary. So Cruz and Kasich have begun focusing on future primaries — especially the May 3 Indiana contest.

Cruz and Kasich on Sunday said they would collaborate to try to block Trump from clinching the nomination before the Republican convention. Kasich said he would focus on New Mexico and Oregon; Cruz on Indiana. The effort is intended to unify anti-Trump voters and minimize his delegate haul in those states.

Pennsylvania provides the trickiest test for Republicans Tuesday because of its unusual rules.

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The statewide winner gets 17 delegates. The other 54 — three from each congressional district — are elected directly by voters. But they are listed on the ballot with no information about which presidential candidate they support. These 54 delegates will go to the convention as free agents, with the ability to support the candidate of their choice.

Even if Trump wins big Tuesday, he still has a distance to go for the nomination. Depending on the results, he would need an estimated 58 percent of the remaining delegates to reach 1,237 on June 7, the day California and four other states vote.