Donald Trump can't lock up the Republican nomination Tuesday -- but he can counter his two opponents' divide-and-conquer strategy and reassert his dominance in the race by running the table in five states.
Hillary Clinton, meanwhile, could finally start to see the finish line. If she's able to handily defeat Bernie Sanders, she could leave the Vermont senator with no real path to the Democratic nomination.
There are 172 Republican delegates at stake, and 384 up for grabs on the Democratic side, when Pennsylvania, Maryland, Connecticut, Delaware and Rhode Island vote Tuesday in the "Acela primary," named after the high-speed train that shuttles commuters up and down the East Coast.
Here are five things to watch in Tuesday's contests:
How big is Trump's win?
The anti-Trump alliance is finally in place. Texas Sen. Ted Cruz and Ohio Gov. John Kasich, Trump's last two foes still standing, have unveiled a divide-and-conquer strategy that will see Cruz focus his efforts on denying Trump a victory in Indiana, a key contest a week away, while Kasich campaigns in Oregon and New Mexico.
His opponents' targets might have shifted, but make no mistake: A sweep would be an important victory for Trump -- and a big step toward the 1,237 delegates he needs to clinch the GOP's nomination.
The Cruz-Kasich alliance only came together, after Trump crushed the competition in New York and then made clear to his opponents that they had no real room in Pennsylvania, Maryland, Connecticut, Delaware and Rhode Island.
Trump's go-to complaint now is that the GOP establishment's only chance of slowing his roll to the nomination is to deny the democratic process and steal it from him.
Of Cruz, Trump told a crowd in West Chester, Pennsylvania, on Monday: "So we're going to pick a guy that over a year got creamed, right? Got creamed. So you explain how that's done. You would have a revolt!"
Whether Trump eventually racks up the delegate count he needs or not, big wins in Tuesday's contests could drive that point home.
Just as important, even with Cruz and Kasich now finally on the same page in an attempt to stop Trump, more big victories could give pause to donors to the #NeverTrump movement.
Clinton looks to lock things up
She won't hit the 2,383 delegates she needs to clinch the Democratic nomination Tuesday. But Hillary Clinton could come close enough to effectively decide the Democratic nomination if she wins big across the Northeast.
Clinton tried to nudge Sanders a bit Monday night in a town hall on MSNBC, noting that she has a much bigger lead right now than then-Illinois Sen. Barack Obama held at this stage over her in 2008.
"It was so much closer than the race right now between me and Senator Sanders," she said.
Clinton also said she's not buying the Sanders campaign's belief that it can catch her in the total vote count when Democrats in delegate-rich California head to the polls in June.
"I am way ahead," Clinton said. "Look, I have the greatest respect for Sen. Sanders, but really, what he and his supporters are now saying just doesn't add up. I have 2.7 million more votes than he has. I have more than 250 more pledged delegates."
Her win in the New York primary last week was a key moment as Clinton denied Sanders his last real opportunity to fundamentally alter the race. On Tuesday night, Clinton can solidify that victory and eliminate Sanders' path to the nomination.
Will Sanders get any good news?
We have been here before.
After Clinton won big on Super Tuesday, she faltered in Michigan. And following her sweep of five big states on March 15, she watched Sanders reel off victories in six out of seven Western contests, slowing her momentum.
On Tuesday night, Sanders hopes for a similar moment to reassert his standing in the race.
Rhode Island looks like a good bet for Sanders, who has performed well in New England -- winning New Hampshire, Vermont and Maine and coming close in Massachusetts.
But he faces long odds in the other four states on Tuesday's calendar.
It could be enough to end his chances at winning the Democratic nomination.
Time is running out for Sanders, whose unexpected and meteoric rise has actually continued: He has now caught Clinton in national Democratic polls, and he has raised more money than she has in the campaign so far. However, those national polls don't mean much now that most states have already voted, leaving him just 12 more contests where he can win delegates after Tuesday.
If he doesn't pull off miracles Tuesday, Sanders will wake up the next day with tough decisions to make about the direction he wants to take the movement he's led.
Will he battle on through California in an attempt to narrow the delegate gap and turn the Democratic National Convention into a bitter battle that he stands little chance of winning? Or will he look to carve out a different role for himself in Democratic politics?
What's up with Pennsylvania?
The Keystone State is set for a chaotic night no matter how the immediate results pan out. That's because 54 of Pennsylvania's 71 directly elected delegates will enter the national convention unbound to any candidate.
Voters in each of the state's 18 congressional districts will pick from a menu of names with no formal indication of whom they plan to support in Cleveland. To help their chances, the Cruz and Trump campaigns have sought out loyal supporters among the ranks of the delegate candidates and distributed those names to voters.
Still, state GOP rules do not bind those would-be delegates to what they tell the campaigns, or anyone else.
In all, more than 160 hopefuls will appear on the ballot Tuesday, with the Cruz campaign pushing for two write-in candidates. Of the more than 135 people who spoke with CNN, about 25% say they'll support Trump, while another 42% say they'll back their congressional district's winner -- good news for Trump, who is poised to win the popular vote by a heavy margin.
Twenty percent of respondents said they will support Ted Cruz, while 11% said they planned to remain uncommitted until a later date, possibly until the convention. None of the candidates told CNN they planned to support Kasich.
The state's rules could make for a chaotic process of sorting out who's really won the state -- and nothing will be certain until the first ballot at the Republican National Convention, anyway, since all 54 of Tuesday night's delegate slot winners will be free to change their minds at any moment.
Can Cruz and Kasich win delegates?
It's all but certain that Trump will romp on Tuesday night. But Cruz and Kasich are hoping to at least pick off a few delegates.
Cruz is eying Maryland as his best chance. The state awards 24 of its 38 delegates to the winners of congressional districts, three apiece. Cruz targeted the state's rural areas, hoping to win one or two of Maryland's eight districts.
Still, Cruz's allies acknowledge Tuesday will be brutal.
"Some of these states -- Connecticut, Rhode Island -- these are Rockefeller-type Republicans. They're not going to resonate with Cruz," state Sen. Michael Hough, the chairperson of Cruz's Maryland campaign told CNN. "Then in May, the map flips back."
Cruz is already in Indiana, a state that votes May 3 and has 58 delegates up for grabs.
Kasich, meanwhile, looks poised to pick up a few delegates in Rhode Island, which awards its 19 on a proportional basis -- and where Cruz might not reach the state's 10% threshold to qualify for any delegates.
He also campaigned hard in Pennsylvania, despite its limited number of delegates available to be won on primary day.
"We're going to have good results across these primaries. I'm very excited about what's going to happen tomorrow," Kasich said Monday in Philadelphia.