John Kasich and Marco Rubio desperately need to win their home states on March 15th – or their paths to the GOP nomination will be a lot tougher. (Peter Stevenson/The Washington Post)

Florida and Ohio are almost always two of the most hotly contested states in American presidential politics — in November, not in March. Or at least, not until March 2016, when Ohio Gov. John Kasich and Florida Sen. Marco Rubio desperately need to win their home states in order to stay in the race to the GOP nomination.

Ted Cruz has his signature (or at least his survival) win in his home state of Texas and has spent the days since Super Tuesday asserting that he is the only candidate who can beat Donald Trump. Rubio won the Minnesota caucuses and finished a close second in Virginia, but he is lagging behind Trump in Florida by almost 20 percentage points, according to the latest RealClearPolitics poll average. Kasich hasn't won a state yet, and he trails Trump by about five percentage points in Ohio.

In other words, Kasich and Rubio both face a do-or-die moment in their home states.

Kasich remains very popular in Ohio despite trailing, and he's made a big bet that upcoming primaries in the Midwest could give him a big boost in delegates. The Ohio GOP primary on March 15 — the first day of winner-take-all states — would be a huge win, if he could pull it off. Rubio doesn't look as strong in Florida, even after former Sunshine State governor Jeb Bush's exit from the race. And unlike Kasich with the Upper Midwest, he doesn't really have a swath of states he's confident about performing well in.

It's partly about optics. Losing one's home state is embarrassing (and you can bet Trump will do everything he can to rub it in, if he wins). But it's also about math. Once the GOP primaries switch to a winner-take-all format, second-place finishes and momentum count for nothing; it's all about delegates. And Florida and Ohio have tons of them — tons of delegates Kasich and Rubio will want to keep out of Trump's pockets.

If Kasich can't win Ohio, and Rubio can't win Florida, their respective paths to the nomination will be something close to impossible.