The Rules Buy Time for Rubio 
 
 The Republican delegate rules, relative to those for the Democrats, are biased toward candidates who win. That makes it very easy to imagine how Mr. Trump could sweep to the nomination over a divided field. 
 
 But that’s not so true before March 15, when party rules prevent states from apportioning their delegates on a winner-take-all basis. Most states wound up splitting their delegates, awarding a pool of at-large delegates proportionally by the percentage of the vote and awarding other delegates to the candidates who lead in each congressional district. 
 
 As a result, it will be difficult on Super Tuesday for Mr. Trump to amass a significant majority of delegates if the other two major candidates — Mr. Rubio and Ted Cruz — clear the thresholds (at highest 20 percent) for earning proportional delegates. It seemed quite possible a few weeks ago that Mr. Trump could build a big lead on Super Tuesday, but Jeb Bush’s exit from the race and the big bump in Mr. Rubio’s poll numbers make it far less likely that Mr. Trump can pull that off. 
 
 Imagine, for a moment, that the candidates fare about as well on Super Tuesday as they have through the first four contests. Given the types of states in play on Super Tuesday, perhaps that yields something like a 34-25-25 percent split between Mr. Trump, Mr. Rubio and Mr. Cruz. 
 
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 In this scenario, Mr. Trump claims a clear edge in delegate accumulation but not a majority. He gets 279 delegates, or just 44 percent of the delegates at stake, while Mr. Rubio receives 164 delegates. 
 
 It’s a respectable tally for Mr. Rubio, even though he loses every state. That’s because he clears 20 percent in every state. That scenario includes Texas, where the most delegates are at stake on Super Tuesday and where Mr. Rubio is in the most danger of missing the delegate threshold because of Mr. Cruz’s home-state popularity. For anyone counting delegates, whether Mr. Rubio reaches 20 percent in Texas is a lot more important than anything else. 
 
 Supposing that Mr. Rubio clears all of these thresholds, he has two big objectives: beating Mr. Cruz in the South, in hopes of driving him from the race, and winning a state or two. His schedule reflects this strategy. He’s visiting a host of Southern states where Mr. Cruz is hoping to do well, and where delegate thresholds still pose some risk to his ability to deny Mr. Trump a majority of delegates. He’s spending all of Sunday in Virginia, which should be one of his best states because of its mix of religious and well-educated voters. Virginia is a clear momentum play (the lift that could come from finally winning); the state uses a purely proportional delegate system, so there are fewer delegates to be gained there than by winning just about anywhere else. Minnesota would seem to be another good option for Mr. Rubio. 
 
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 The deficit for Mr. Rubio after Super Tuesday in this scenario — 181 over all and 115 from Super Tuesday — would not be especially big. If Mr. Rubio won Florida — a winner-take-all state worth 99 delegates — it could balance out nearly all losses from Super Tuesday. 
 
 Then All Eyes Are on March 15 
 
 But for the same reason Mr. Rubio can erase so much damage by winning in Florida on March 15, he can’t afford to lose on March 15 either. 
 
 Ohio and Florida will award their delegates on a winner-take-all basis. Missouri will award its delegates on a winner-take-all basis by congressional district, and Illinois isn’t much different. North Carolina, on the other hand, awards its delegates proportionally. It figures less prominently in the delegate math and as a result the candidates are unlikely to spend money there on television advertisements or campaign stops. 
 
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 If Mr. Trump swept the day in the same way he is expected to sweep Super Tuesday, he would net nearly three times as many delegates as he would on Super Tuesday, defeating Mr. Rubio, 282 delegates to 40. For Mr. Rubio, winning Florida would make Mr. Trump’s advantage a more manageable 183 to 139, but his hole would start looking pretty deep. 
 
 With that sort of a deficit, Mr. Rubio’s chances of winning a majority of delegates would all but evaporate. 
 
 Even if Mr. Rubio swept on March 15 and started doing as well as Mitt Romney did at that stage in 2012, he would barely edge ahead of Mr. Trump in the pledged delegate count. And of course, there would be plenty of reason to question whether Mr. Rubio could really do so well after losing so many states to that point. 
 
 Delegate Math Isn’t The Problem 
 
 Winning by March 15 is what matters for Mr. Rubio, not the math. 
 
 It’s not going to be easy. The Republican establishment is flocking to him, but the escalating pace of the primary season makes it harder for him to take advantage of growing support from the party. There’s not much time for him to raise money, and whatever he does raise will be spread fairly thin. 
 
 The party isn’t fully unified either, with Mr. Cruz and particularly John Kasich remaining in the race. Mr. Trump holds between 30 and 40 percent of the vote, most national surveys say, so it is very difficult for Mr. Rubio to overtake him when votes are siphoned off by another candidate. If Mr. Kasich remains in the race, his home state of Ohio will be very difficult for Mr. Rubio to win. 
 
 There’s a final issue: Some big winner-take-all and winner-take-most states aren’t necessarily favorable ground for him. 
 
 The Winner-Take-All States Seem Promising for Trump If the rest of the country votes the way the first four states did, Donald Trump will have an edge in the big winner-take-all contests. New Jersey Delaware Florida Ohio United States Arizona Montana South Dakota Nebraska 43.6 40.2 39.4 37.0 35.3 33.9 31.5 30.5 27.8 
 
 Mr. Trump has tended to fare best with less educated and less religious voters. There’s also evidence he does better in places with a larger nonwhite population. Florida and Ohio fit the bill. And separately New Jersey also shapes up well for him later in the calendar. They’re all projected to be above-average states for Mr. Trump based on the results so far (though obviously this can change, and it doesn’t account for a potential home-state edge for Mr. Rubio in Florida and Mr. Kasich in Ohio). 
 
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 New Quinnipiac surveys show Mr. Trump ahead in Ohio and Florida. 
 
 Rubio Needs Others To Quit 
 
 But there is one important bit of good news for Mr. Rubio: the struggles of Ted Cruz. He has finished third in two consecutive contests where he had hoped to perform well. He is in danger of being shut out on Super Tuesday; he could even lose his home state, Texas. Polls show him falling behind Mr. Rubio in other Southern states like Georgia and Oklahoma. 
 
 The Cruz campaign has always been clear that it is counting on a strong showing on Super Tuesday, and Mr. Cruz’s path to the nomination would look exceptionally bleak if he fared as poorly on March 1 as he did in South Carolina and Nevada. It could be enough to force him from the race. Mr. Kasich’s play is less clear, but he could quit if he finishes poorly in Michigan on March 8. 
 
 If Mr. Cruz or Mr. Kasich exited, it would give Mr. Rubio the chance to build a coalition of ideologically consistent conservative voters and more mainstream, well-educated conservatives. The onset of a real one-on-one race would pose a challenge to Mr. Trump, who would finally be forced to build a majority coalition. 
 
 So far, more G.O.P. voters tell pollsters they would definitely oppose Mr. Trump than currently support him, which at least raises the possibility that Mr. Rubio could prevail in a one-on-one fight. Polls pitting the two against each other have shown a tight race or even a lead for Mr. Rubio. 
 
 Mr. Trump would also have to overcome a barrage of negative television advertisements — something he hasn’t had to face very much of so far. 
 
 Whether Mr. Rubio could in fact consolidate the preponderance of Mr. Kasich or Mr. Cruz’s supporters is hard to say. 
 
 But whether it happens before March 15 could easily decide the outcome of the Republican race. ||||| With just five days until Super Tuesday, time is growing perilously short for the Republican “establishment” — whatever that means these days — to stop the Donald Trump train from picking up even more speed. Five days is two fewer than God had to make the world and all its creatures, and if you have looked at Trump’s poll numbers lately, the establishment’s task might seem equally gargantuan. 
 
 But there are a couple of places where Trump looks vulnerable. Where? We don’t have polling for every Super Tuesday state, and certainly not enough to drill down beneath state-level data. But here’s one clue: Where is Team Rubio buying TV time? The answer: Virginia, Georgia and Texas. His PAC has splashed out over $1.5 million in these key Super Tuesday states and appears focused on the establishment’s backyard as well — Virginia’s Washington, D.C. suburbs. 
 
 According to our most recent polls-plus forecast, Rubio, recently crowned prince of the GOP donor class, has a 43 percent chance of winning Virginia on Tuesday, a slight advantage over Trump. The D.C. suburbs in northern Virginia are home to many who make their living working, directly or indirectly, for the government. Like most large metropolitan areas, the District of Columbia and its suburbs tend to break for Democrats in general elections, but the area has sizable pockets of Republican voters. In 2012, 40 percent of Fairfax County and 30 percent of Arlington County voted for Mitt Romney. 
 
 Since Tuesday, a Rubio PAC, Conservative Solutions, has spent $245,430 in the D.C. media market for ads set to air through Tuesday’s primaries. And the PAC has spent over $144,000 in the rest of the state, focusing its buys in the Virginia Beach/Norfolk area, along with Richmond. (The Rubio campaign itself has made modest buys in Virginia Beach/Norfolk, though not in the D.C. metro area.) 
 
 And in Georgia, where we give Rubio a 29 percent chance of winning (compared with 64 percent for Trump), the Rubio PAC just dropped $455,258 in the Atlanta media market. Hotlanta indeed. 
 
 Where else is the money going? Texas — including Houston, Ted Cruz’s fortress of Constitutionalism and cowboy boots. Conservative Solutions spent a whopping $689,302 on ads to air over the next few days in Dallas, Austin, Houston, and San Antonio. 
 
 And what about Trump? Not a major ad buy in sight. 
 
 UPDATE (Feb. 25, 3:19 p.m.): Rubio’s chances of winning in Virginia and Georgia have been updated to reflect new polls in those states.
– Whether Marco Rubio's aggressive performance in Thursday's debate translates into success on Super Tuesday remains an open question, but the Upshot blog has some hopeful news for his campaign: Even if Donald Trump sweeps all the states in play—and polls suggest he has a decent chance of doing that—Rubio remains very much alive. The main reason is that Republicans forbid winner-take-all contests prior to March 15, meaning Rubio (and Ted Cruz) can still pile up delegates for second and third place. The blog floats the possibility of Trump winning the day with a 34-25-25 percent split over the other two, in line with his previous victories. That would give him 279 delegates and Rubio 164. "It’s a respectable tally for Mr. Rubio, even though he loses every state," writes Nate Cohn. Ideal? No, but it keeps him afloat until March 15, when big winner-take-all states such as Illinois, Ohio, Missouri, North Carolina, and Rubio's home state of Florida come into play. At this point, Rubio would have to win some of those to have any hope of beating Trump. If not, his "chances of winning a majority of delegates would all but evaporate." Of course, Rubio hopes to pull off some victories on Tuesday, and FiveThirtyEight notes that his campaign is spending heavily in Virginia and Georgia to make that happen. He's also spending big in Texas, which has the most delegates at stake, for a different reason. Because it's Cruz's home turf, Texas is where Rubio is most vulnerable to failing to receive 20% of the vote, the threshold for receiving any delegates at all.