That's it. It's settled. There's no turning back. Marco Rubio has given up his presidential bid. Done. Finished.

Unless…

Rubio comes roaring back from his utter ruin in Florida to share the ticket with Ted Cruz.

Yes, it's crazy. But this is a crazy election.

Let's get some things straight. Rubio did not lose his home state, and did not drop out of the race, because an angry electorate was too resentful to bask in the warm glow of his political talent and ambition. He lost because his ambition exceeded his talent — leading him to run prematurely as the rightful heir to the Bush legacy, more rightful even than Jeb Bush himself. Rubio wasn't seen unfavorably as a person or a Republican so much as he was dismissed as a candidate.

But Rubio's departure from the race does not alone signal the death of his brand of Bushism. Although John Kasich has run as Casper the Friendly Ghost, emitting a gauzy and comforting spectral togetherness, he is actually the most concretely Bush-like — at least on domestic issues — in his stubbornly compassionate conservatism. Even Donald Trump is poised to attract more Bush-era has-beens who want to be influential again, perhaps in virtue of Trump's exceedingly post-9/11 view of protection and security.

Which brings us to Ted Cruz, poised to become the most influential conservative leader in the country — especially, but not only, if he wins the nomination. On the surface this is not such a bad thing. But it comes with potentially major burdens: like Marco Rubio. For the minute it became clear to Republicans what to do with Rubio during the campaign — namely, squeeze him out — the question of what to do with him afterward arose.

And here it is: Bloodied but still more than capable of delivering the kind of speech that makes most Republicans stand up and cheer, Rubio has just enough of a constituency, and just enough of a brand, to make a plausible claim to the vice presidential slot. (Yes, if Trump wins, this is all spectral gauze, but stay with me.) He's got some crucial delegates. He's got some killer head-to-head polls with Clinton. Squint from a certain angle, and he looks a whole lot like a weaponized, next-generation Dan Quayle. In point of fact, Marco Rubio is classic modern-day GOP veep material.

That doesn't mean Cruz needs him. Aside from the ability to deliver incredibly good-sounding speeches that ultimately do nothing, I suspect many Republicans will concede that, on paper at least, Kasich has Rubio beat in the veepstakes. But Rubio has a trump card: the established party leadership.

That's right. For all his half-cloaked conventionalism, Kasich is no darling of the right's Beltway power brokers. On foreign policy, he is seen as profoundly anodyne, if not as an outright fool. Here Rubio has a powerful advantage. Heading into Cleveland, his backers will say, even if neither Cruz nor the ticket needs Rubio, the party needs him. He is, after all, the future — an emblem of where the GOP must go and isn't already. Cruz may sit at the center of gravity. Kasich may orbit nearby. But only Rubio, the logic goes, represents the momentum Republicans have no governing future without.

Through this door, Bushism can return. For all his accumulating power, Cruz very well may find himself too exhausted from beating back Trump to repel Rubio too. There may be no viable option in Cleveland aside from conceding him the bottom of the ticket. Come to think of it, there may be no real alternative now. Cruz needs votes, and he can hoover them up from Rubio's jilted supporters more easily than Kasich's, for the simple and galling reason that Kasich is not dropping out. Sure, striking a deal with Rubio now gives away some power up front — not a very Cruz move. But it goes a long way to ensure he'll head into the convention with as much power as possible.

That's why we need to game out these moves today, regardless of whether Trump wins it all. The heat is on Cruz to do what it takes to maximize the party's chances of dispatching the Donald — who, after all, is getting in the habit of racking up 40 to 45 percent victories. It is challenging but not impossible for the party to look legitimate knocking out a frontrunner who lacks majority support. But the margin for error is ice-thin.

Cruz is already well-advised to consolidate his Beltway cred by linking up with the reform conservatives who lived through the Bush years and learned best how to get over them without going on a political bender. Whether he can let them into the anti-Trump tent without prompting a stampede of Bushites, Rubio included, will be his biggest test of leadership yet.