Five major states hold primaries on Tuesday – Florida, Ohio, Illinois, North Carolina and Missouri – and hundreds of delegates are up for grabs. It's also the first time huge troves of delegates are at stake in winner-take-all Republicans contests.

For Republicans, the day could shape up to be a last gasp of the establishment as it searches for a way to halt Donald Trump’s march to the nomination. And for Democrats, it could be another troubling sign that the party has failed to coalesce around Hillary Clinton.

Here’s a look at what could be the most pivotal day in the primary calendar:

A home-state last stand. Florida should be a bastion of support for U.S. Sen. Marco Rubio, but polls show him badly trailing front-runner Donald Trump in his home state. Ohio Gov. John Kasich is doing better in his backyard, but he's also under enormous pressure to win his first state Tuesday or go home. All 99 of Florida's delegates are up for grabs, and Rubio will likely be forced to drop out should he lose. Ditto for Kasich in Ohio, where 66 delegates are at stake. Read more here.

More Michigans in the making? The Big Upset is never far from the minds of Vermont U.S. Sen. Bernie Sanders and his supporters. His surprise victory over Hillary Clinton in Michigan last week breathed new life into his campaign against the former secretary of state, which had taken on an air of inevitability as she built a daunting delegate lead. Clinton seems poised to win handily in Florida and North Carolina, but Sanders hopes that his win in Michigan will reverberate in the delegate-rich industrial Midwest states set to vote Tuesday. Unlike the GOP contest, the Democratic delegates are still awarded proportionally, meaning that both Clinton and Sanders could finish with relatively comparable hauls by the day's end. Read more here.

Donald Trump's knockout punch. The violence that erupted this weekend in Chicago and elsewhere as protesters ratcheted up their opposition to Trump only reinforced the mainstream Republican opposition to the billionaire. Yet strong showings in the spate of states that vote Tuesday could make his already daunting delegate lead become insurmountable and force his opponents to put all their hopes on a delegate fight at the Republican National Convention in July. Already, there are efforts underway to prime the ground in Georgia for a Trump alternative. Read more here.

Ted Cruz's big day. Texas U.S. Sen. Ted Cruz may not win any of Tuesday's contests, but he could emerge a winner in his own right. A Rubio defeat and a Kasich letdown would make Cruz, who has long argued he's the only candidate capable of beating Trump, the undisputed leading contender to the title. He has, after all, won far more states than any other Trump challenger, including his home state of Texas earlier this month. Some Republicans who have long fought Cruz are beginning to reluctantly embrace him. Even if Kasich and Rubio survive Tuesday's votes, look for Cruz and his allies to step up the case that he's the only candidate not named Trump who should stay in the race.