-- Voters in four states will head to the polls today to pick a presidential nominee.
Of these four states, the stakes are significantly higher in Michigan.
Michigan is the biggest prize today for both Republican and Democratic candidates.
Sanders Needs a Win
As of now, Hillary Clinton has 1,130 delegates, including pledged delegates and superdelegates, while Bernie Sanders only has 499.
With Clinton expected to sweep the Mississippi primary -- the only other Democratic contest today -- Sanders needs a win in Michigan to narrow the delegate gap between him and Clinton.
Michigan officials anticipate voter turnout to reach historic highs, The Associated Press reports, and Sanders believes, “if there is a large turnout, we are going to win here in Michigan.”
But Michigan, Ohio’s neighboring state, is essential for the struggling candidate, who has yet to score a win and has the smallest amount of delegates.
"The road to Ohio in this case leads through Michigan," Kasich’s chief strategist John Weaver told ABC News in February.
During the South Carolina primaries, Kasich was already focusing on Michigan, campaigning heavily there and pouring a lot of resources into the state.
Michigan's primary was once the do-or-die moment for Kasich. Back in Feb. 15, at a town hall in Allendale, Michigan, Kasich told Grand Valley State University students: “We have to do really, really well in this state, I mean -- or I have to roll up the carpets and go back.”
Now, his campaign is blasting out the narrative that Kasich is surging in Michigan, pointing to his performance in Thursday’s GOP debate in Detroit, hosted by Fox News.
Rubio Stuck in Third Place
The Florida senator’s chances of being the Republican alternative to Trump may have slipped away this past weekend.
Despite nabbing a (much needed) win in Puerto Rico, earning him 23 delegates, Rubio’s main rival, Ted Cruz, solidified his second place spot in the GOP race after coming out on top in Kansas and Maine.
In an NBC/WSJ/Marist poll released Sunday, the Florida senator takes third place in the Wolverine State with 17 percent support, compared to Trump’s 41 percent and Cruz’s 22 percent.
While Rubio isn’t expected to win any of today’s state primaries and caucuses, he is confident his campaign will succeed in his home state of Florida.
Robocalls From One (Former) Governor, For Another
“Hello, this is Mitt Romney calling, and I’m calling on behalf of Kasich for America,” the recording starts out. “Today, you have the opportunity in Michigan to vote for a Republican nominee for president. These are critical times that demand serious, thoughtful commander in chief.”
While the former Massachusetts governor and 2012 GOP presidential candidate hasn’t formally endorsed any candidate, his efforts show the GOP establishment goal is to stop Trump from becoming the nominee.
“If we Republicans were to choose Donald Trump as our nominee, the prospects for safe and prosperous future would be greatly diminished,” Romney says in the recording.
ABC’s Alana Abramson and Ben Gittleson contributed to this report.