If Donald Trump wins the Florida primary on March 15, he will have sewn up the GOP nomination. The odds are that he will win the Sunshine State, where the latest polls show him at 40%, 21 points ahead of second place in the Real Clear Politics average. Moreover, Trump enjoys an advantage over his three remaining challengers. He can operate on offense, while each of his challengers is tied down defending home turf in must-win contests.

Senator Cruz must win the Lone Star State on March 1. On March 15, Ohio is do-or-die for Governor Kasich, as is Florida for Senator Rubio. For Mr. Rubio, Jeb Bush’s withdrawal is a mixed blessing. Without Jeb, the only excuse for not winning home turf — namely that Messrs. Rubio and Bush would split the anti-Trump vote — has disappeared,.

If Mr. Trump wins any of these states, the home-state challenger will be severely hobbled, and Mr. Trump will become almost unstoppable. So look for Trump to spend much of next week at Texas, the biggest prize in the so-called “SEC Primary,” in which almost 700 delegates will be up for grabs in nine primaries, three caucuses, and one convention.

Mr. Trump will be seeking to defeat Mr. Cruz in his own nest, which is not so Cruz-friendly as it might seem. Texas is an open primary, and Mr. Trump seems to have more appeal to independents and working class Democrats than right-wing Mr. Cruz. Texas and the other SEC states, moreover, award delegates proportionately.

As a result, even if Mr. Cruz defends Texas successfully, he will have to share its 155 delegates with his rivals. On the other hand, if Mr. Cruz loses to Trump, he will sustain a psychological blow, likely leading to a gradual decline thereafter. From Mr. Trump’s perspective, he has no real downside, as, whatever happens, he is likely to haul in a respectable number of Texas delegates.

Florida and Ohio are different. On March 15, the Sunshine State will award all 99 of its delegates to the winner, as will the Buckeye State its 66 delegates. If Mr. Trump claims winner-takes-all Florida, it will be over for Rubio. So too for Mr. Kasich, who is unlikely to amass a significant number of delegates before then. In face of a Trump win in the Sunshine State, even a Kasich win in Ohio would result in a net loss between the two states of about 35 delegates for Mr. Kasich relative to Mr. Trump. So, Mr. Kasich would simply be too far behind at that point to catch Mr. Trump.

Here are the rough numbers. In the three contests so far, Mr. Trump has taken 40% of the approximately one million votes cast for the four candidates combined (this analysis considers Ben Carson a drop-out). If he continues at a 40% level through March 14, he will win about 460 delegates out of Nevada’s 30 delegates in play today, the 770 in the SEC contests and the 350 available in the eleven contests between March 5 and 12. Added to his current 67, he’d have 527 delegates.

Messrs. Cruz and Rubio have averaged roughly 25% of the combined vote for the four. If both continue at 25%, each would amass about 275 by March 14. That leaves 10% of the votes “stranded” with Mr. Kasich, who cannot win, even with a victory in Ohio, where today’s Quinnipiac poll shows Mr. Trump leading Mr. Kasich by 5 points.

So, it is Florida that matters, and Florida is not so Rubio-friendly as you might think. Florida is a closed primary in which only Republicans can vote. That runs counter to the whole rationale of Mr. Rubio’s current campaign, i.e. that he is the “crossover candidate” around which the “GOP establishment” must rally to have any chance to win in November. Well, no “crossing over” is permitted in a closed primary.

If Mr. Trump wins Florida’s 99 delegates, his likely delegate total will increase to about 625, more than double the totals of Messrs. Rubio and of Cruz. Including the 270 delegates up for grabs in the five other contests on March 15 (including Ohio), there would be only 1,220 delegates remaining to be claimed. With only 275 delegates each, either Messrs. Rubio or Cruz would have to collect about 960 delegates, or 80%, to win outright. This is hard to imagine.

So, if Mr. Trump wins Florida, he will win the nomination. If either Mr. Rubio or Mr. Cruz wins, he would have about 375 delegates, close enough to compete with Trump at 527… but only if the other candidates drop out. All, again, depends upon Florida. A Trump win in Florida dooms Messrs. Rubio and Kasich, and renders the odds insurmountably long for Mr. Cruz.

Then, again, too, Mr. Trump could ignore this analysis and camp out in Alabama and Georgia until March 1 and seize their 126 delegates, instead of going toe-to-toe with Cruz in Texas, where today’s University of Texas/Texas Tribune poll shows Mr. Cruz leading Mr. Trump 37 to 29.

Mr. Trump could then move to Illinois and Missouri, winner-take-all states with a combined total of 121 delegates at stake on March 15th, and, by winning them, come out even better than winning in Florida. With his strategic advantage, Mr. Trump is likely to go all the way.