Republicans Marco Rubio and John Kasich are fighting for their political futures Tuesday, desperate for wins in their home states of Florida and Ohio to keep their White House hopes alive and complicate Donald Trump's path to the nomination.
Democratic front-runner Hillary Clinton is hoping to keep rival Bernie Sanders from building new momentum in the Midwest.
With more delegates up for grabs than almost any other day in the primary calendar, Tuesday's contests afford Trump and Clinton the chance to put their parties' nominations out of sight for their competitors. While Florida and Ohio are the biggest prizes, Missouri, Illinois and North Carolina are also awarding a cache of delegates.
More than 1,000 delegates are at stake (358 for Republicans and 691 for Democrats) in five states, and the voters in Tuesday's primaries have the chance to dramatically impact the Republican and Democratic races.