Tim Alberta explains at National Review Online how today’s primary elections could determine the outcome of the Republican presidential race.

Tuesday’s primaries represent the last stand not only for John Kasich and Marco Rubio but also for Republicans hoping to halt Donald Trump’s march to the nomination.

A total of 361 bound delegates are up for grabs on March 15, with contests in five states — Florida, Illinois, Missouri, North Carolina, and Ohio — as well as the tiny Northern Mariana Islands, which award all nine of their delegates to the winner. North Carolina is proportional, and the rules in Illinois and Missouri are such that their delegates are likely to be split, barring a dominant performance by one candidate. That means that Trump, who leads the delegate race by nearly 100 over Cruz and 400 over Rubio, can put a stranglehold on the nomination if he carries Tuesday’s grand prizes, winner-take-all Florida and Ohio, which award 99 and 66 delegates respectively.

Trump victories in those two states would almost certainly eliminate both Kasich and Rubio while stretching his lead over Cruz to at least 300 delegates. At that point, the billionaire front-runner would be well more than halfway to the 1,237 delegates needed to clinch the GOP nomination, and Cruz would find it nearly impossible to prevent him from getting there, for two reasons: The race heads into Trump-friendly territory in April and beyond; and contrary to popular belief, many of the states voting after March 15 are not winner-take-all, meaning that Trump will continue to collect plenty of delegates even in contests where Cruz defeats him head to head.