Hillary Clinton and Donald J. Trump have drawn closer to their parties' nominations with almost every passing week. The five elections on Tuesday — in Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island — may offer them their best chance before June to gain a final, decisive advantage over their opponents.
But Senator Bernie Sanders of Vermont has been a tenacious opponent on the Democratic side, and could find precincts of strength even on a Primary Day that favors Mrs. Clinton. Gov. John Kasich of Ohio and Senator Ted Cruz of Texas face even more daunting terrain on the Republican side; for them, this week is a battle for survival.
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Here are some of the big questions we will be watching as the returns roll in:
Can Clinton effectively claim the nomination?
It would be almost impossible for Mrs. Clinton to amass enough delegates on Tuesday night to clinch the Democratic nomination, even including superdelegates. But if she manages a commanding performance across the Northeast, following her strong victory in New York last week, she could come close enough to declare the race all but finished.
Mrs. Clinton and her supporters have handled Mr. Sanders cautiously, even as she has gained a clear upper hand. In the event that she sweeps the Tuesday contests, there may be growing public pressure on him from across the party to scale back his campaign — or wrap it up entirely — before the political calendar moves into a string of Sanders-friendly states in May.
Will any city vote for Sanders?
Mrs. Clinton's greatest strength in the primary has been her support from black and Hispanic voters, partisan Democrats and older women of all backgrounds. These groups are often most powerful in big cities, and Mrs. Clinton's winning record has often correlated with the strength of the urban vote: She won Illinois thanks to Chicago and Nevada thanks to Las Vegas, and took New York by 15 points thanks to New York City.
If she keeps up that streak in Baltimore, Bridgeport, Philadelphia and elsewhere on Tuesday, Mr. Sanders could wind up getting crushed. His best shot at avoiding a shutout might be Rhode Island, with Providence and its sizable student population as a lifeline.
Can Trump win a Pennsylvania blowout?
Mr. Trump is expected to carry Pennsylvania easily, but the state's quirky delegate rules mean winning isn't everything — or even the most important thing. Pennsylvania will award only 17 delegates to the winner of the popular vote statewide; it will send an additional 54 unbound delegates to the convention in Cleveland, all of them free to vote for their own preferences.
For Mr. Trump, those 54 delegates could be the difference between winning the Republican nomination on the first ballot and falling agonizingly short. The bigger his margin of victory is on Tuesday, the stronger his hand will be in coaxing and cajoling the whole contingent from Pennsylvania into his camp.
Will Kasich and Cruz split evenly?
With Mr. Trump favored to win all five states voting on Tuesday, the challenge for his two opponents is once again to hold down his margin of victory and snatch away whatever delegates they can. That task is most urgent in Connecticut, Maryland and Rhode Island, three states that lean strongly to Mr. Trump but where many delegates are awarded according to the vote in each congressional district.
In theory, that could give Mr. Cruz and Mr. Kasich the opportunity to peel off delegates from Mr. Trump here and there, even as Mr. Trump wins easily over all. But that game plan did not work in New York: Mr. Cruz and Mr. Kasich split the anti-Trump vote and failed to make a real stand in any region of the state. Mr. Trump won in a rout.
Which Trump will take the stage?
The Republican front-runner gave a sober victory speech — by his standards — in New York last week, fueling speculation that he would shift his candidacy in a more conventional direction. Within days, he was back to branding Mr. Cruz as "Lyin' Ted" and mocking his Canadian birthplace. On Monday, Mr. Trump ridiculed Mr. Kasich for the way he eats. (The governor, Mr. Trump claimed, takes excessively large bites of food.)
For Mr. Trump to sew up the nomination without a messy spectacle at the convention, he has to do more than amass delegates. He also has to convince his Republican critics — or at least, any of them who remain persuadable — that he is not some political wild man who will trash the party in the general election. That means adopting a different tone on election night — and sustaining it this time.