It isn't quite "Super Tuesday," but voters in five states are taking part in key primaries to decide which Democrat and Republican will compete in the November presidential election.
Why is it important?
After Tuesday, more than half of the 50 U.S. states will have held their nominating contests, so trailing candidates are running out of time to catch front-runners Donald Trump and Hillary Clinton. The next time nearly as many delegates are available on one day is June 7 when it may already be too late.
Up for Grabs Tuesday
Florida: Republicans 99 (winner take all), Democrats 246
Ohio: Republicans 66 (winner take all), Democrats 159
Illinois: Republicans 69 (winner take most), Democrats 182
North Carolina: Republicans 66, Democrats 121
Missouri: Republicans 52, Democrats 84
At Stake for Candidates
Florida Senator Marco Rubio: Far behind in delegates, he needs the 99 from his home state to have a chance. A loss could mean he drops out.
Ohio Governor John Kasich: Facing the same long odds as Rubio, he is banking his campaign's future on Ohioans delivering him 66 delegates.
Texas Senator Ted Cruz: Says he is the only one who can beat Trump, but if polls hold, Cruz gets no delegates from Florida or Ohio and only a second-place portion from Illinois, Missouri and North Carolina.
Businessman Donald Trump: Winning both Florida and Ohio would really distance him from the field, but either way he should finish Tuesday more than halfway to clinching the nomination.
Former Secretary of State Hillary Clinton: A stack of wins further solidifies her hold on the nomination with proportionate delegate math helping keep her there.
Vermont Senator Bernie Sanders: Needs to start winning states with big margins to catch up, but anywhere he loses Tuesday has to at least be close to keep Clinton in range.