Marco Rubio enters Super Tuesday in a desperate fight for survival, not only his own but the GOP establishment’s as well. He is their last hope to deny the party’s nomination to Donald Trump. The nominee will be determined between Super Tuesday and March 15, by which time 60 percent of the national convention’s 2,470 delegates will be chosen.

So, how is the race likely to unfold over the next two weeks? Most assessments look ahead to the candidates’ prospects in individual states. But the states’ primaries and caucuses do not happen in a vacuum. They occur in the context of preceding contests in which candidates gain or lose momentum and eventually create a sense of inevitability or take on the aura of a deathwatch. And in the 2016 campaign, the GOP’s primary rules and schedule are driving the race in ways that are unprecedented.

The sequence of primaries and caucuses over the next two weeks will have a profound effect on the prospects of Trump, Rubio, Ted Cruz, and John Kasich. After three landslide victories, Trump has formidable momentum going into tomorrow’s primaries. Most of these contests are in deep red states, favorable terrain for him, and the delegate allocation rules in these states will enlarge his delegate haul beyond what is expected.

A sweep tomorrow will set Trump up to run the tables in six red-state primaries over the next 11 days and effectively seal the nomination on March 15. To prevent this outcome, Trump’s opponents must limit his momentum, fend off challenges by their other rivals, and win enough delegates to remain viable.

It’s a tall order.

Fourteen states will hold primaries or caucuses tomorrow. Eight of these states are deep red, better for the outsiders, Trump and Cruz, than the insiders, Rubio and Kasich. Four states are blue or purple and are thought to be friendlier to Rubio and Kasich. Two other states hold caucuses that elect delegates who are officially unbound to any candidate.

Recent polls are available in eight of the 12 states that elect delegates bound to candidates tomorrow. In the states that seem best suited for Rubio and Kasich, mid-February polls find Trump holding big leads over Rubio—26 points in Massachusetts and 15 points in Vermont. In more bad news for Rubio, Kasich is close enough to beat him in both states.

In five deep red states voting tomorrow:

An Oklahoma poll conducted last week shows Trump at 29 percent, leading Rubio by eight points and Cruz by nine.

In Alabama, a late-February poll finds Trump at 36 percent, with Rubio at 23 percent and Cruz at 16 percent.

In Georgia, the Real Clear Politics’ average of four polls taken in the past week has Trump, at 35.3 percent, leading Rubio by 13.5 points and Cruz by 15.8 points.

In Tennessee, Trump lead in a late-February poll with 40 percent, and Rubio trailing at 19 percent and Cruz at 22 percent.

In Virginia, two late-February polls find Trump with 40.5 percent, Rubio at 27 percent, and Cruz with 16 percent.

In Texas, RCP’s average of six polls taken February 19 – 26 has Cruz opening a lead with 35.9 percent, Trump at 27.3 percent and Rubio with 18 percent. With 155 delegates at stake, Texas is Super Tuesday’s big prize. The state requires candidates to win at least 20 percent of the vote to qualify for delegates. With early voting well underway, Rubio is two points shy of qualifying, while Cruz and Trump are well above the threshold. If Rubio fails to reach 20 percent, he’ll receive no delegates and his share will be divided between Cruz and Trump. If he does make the threshold, he’ll deliver a blow to Cruz by denying him a significant haul of delegates in a state that will determine whether the Texas senator survives.

Super Tuesday is likely to be a rough day for Marco Rubio. He has no good ground on this battlefield, even in states where conventional wisdom suggests he should be strong. In fact, he might even lose to Kasich in these states, and narrow wins over Kasich might be counted as losses, considering Rubio’s advantages in money, endorsements, and organization.

Between Super Tuesday and March 12, eight states and three territories will hold primaries or caucuses. Six of the states are deep red. Only two, Michigan and Hawaii, might be considered hospitable to Rubio. In Michigan, two late-February polls have Trump at 41 percent and Rubio at 18 percent, with Cruz close at 15 percent. This is very bad news for Rubio. The Michigan primary is on March 8, one week before the crucial contests in Florida, Ohio, Illinois, and North Carolina. A loss of this magnitude in a state that seems fertile ground for Rubio would be crippling after having struggled through Super Tuesday.

So Rubio is likely to limp into the March 15 primaries, and his prospects aren’t any better in these states. He is in fourth place in Ohio, and trails front-running Trump by 18 points. Ohio is winner-take-all, so Rubio is likely to be shutout of the delegate count. In Illinois, another winner-take-all state, Rubio trails Trump by 15.5 points in two late-February polls, with Cruz only two points behind. In North Carolina, three mid-February polls show Rubio trailing Trump 31 percent to 17 percent, with Cruz in second place with 19 percent.

But the worst news for Rubio comes from his home state of Florida, where two late-February polls have him trailing Trump 44.5 percent to 26.5 percent. Rubio appears to have benefited from Bush’s withdrawal, but Trump is rising, too. Even if Kasich were to leave the race and Rubio inherited all of his support, he’d still trail Trump by 11.5 points. A loss in Florida would end Rubio’s campaign.

This raises a question getting a lot of attention now: which candidates benefit most as others drop out? A mid-February NBC/Survey Monkey tracking poll found that Trump was the second choice of 12 percent of GOP voters, while Cruz was favored by 18 percent and Rubio, by 17 percent. Much has been made of the fact that Cruz and Rubio benefit more than Trump from these second-choice preferences.

That’s true enough, but more significantly, the poll debunks a myth that has persisted for months—that Trump’s support is capped at around 30-35 percent. The source of this myth seems to be that state and national polls have shown Trump bumping up against a ceiling of around 30-35 percent. But these assessments ignore the fact that he is competing with other candidates for some of the same voters and that, as the field narrows, his support will rise. The NBC/Survey Monkey poll found Trump with 38 percent of the GOP vote, so adding his second-choice support brings him closer to 50 percent. Moreover, recent polls show Trump is already close to, or above, 40 percent in Florida, Georgia, Michigan, Virginia, Illinois, New Jersey, West Virginia, Tennessee, and Massachusetts. And, of course, he won Nevada with 46 percent of the vote.

The candidates’ prospects beyond March 15 are cloudy, at best. Many analysts say Rubio—or Kasich, if he survives—will fare better in these states. Recent polls suggest otherwise. Trump leads Rubio by 10 to 25 points in New York, West Virginia, and Wisconsin, and Cruz is in position to beat Rubio for second place in all three states. Only Pennsylvania and Utah offer anything like good news for Rubio.

The landscape is unrelentingly bleak for Rubio. He is even at risk of being knocked out of the race by Kasich. If Kasich beats or stays close to him in the establishment-friendly states voting before March 15, Kasich could gain momentum and overtake Trump in Ohio. If Rubio is unable to close Trump’s 18-point lead in Florida, Kasich might emerge as Trump’s only marginally viable rival after March 15.

In desperation, GOP elites and mega-donors are finally coalescing behind Rubio. No doubt, Kasich would enjoy the irony if he were to outlast their anointed candidate. That alone might be reason enough for him to stay in the race.

The leadership of the GOP has three choices now. They can pull out the stops to deny Trump the nomination, one way or another. Senate Majority Leader Mitch McConnell, among others, is already exploring these options. If they attempt and fail, they will shatter the party. If they succeed, Trump is likely to retaliate by making an independent bid for the White House, virtually ensuring a massive defeat for the GOP in November, including loss of the Senate and perhaps even their House majority.

Or the institutional GOP can cede the nomination to Trump, distance itself from him, and free down-ballot candidates to run against him or with him as they choose. In practice, if Trump is the nominee, many GOP candidates are likely to take this course whatever the national party decides. In fact, this is already underway. This strategy might save some incumbents but at what cost to the GOP as a functioning political party?

Or the party elite can embrace Trump as their standard bearer, as some are already doing, hope for the best, and risk damaging the conservative brand the GOP has skillfully crafted over four decades. Trump would surely lose in November, probably taking GOP control of the Senate down with him—or so says conventional wisdom. But what if Trump wins? What, then, would become of the GOP brand after four years of a Trump presidency?

Philip Diehl is a former chief of staff of the U.S. Treasury Department, staff director of the Senate Finance Committee, and director of the U.S. Mint.