Marco Rubio has been remarkably upbeat in the wake of primary losses. Now he's staking everything on Florida. (Peter Stevenson/The Washington Post)

After a disastrously bad series of results in Tuesday's primaries and caucuses, the end is near for Marco Rubio's hopes of being the Republican presidential nominee.

The senator from Florida continues to insist that he will stay in at least through his home-state primary next Tuesday, casting himself as the only thing standing between rival Donald Trump and the GOP nomination. But polling suggests that a Florida win is far from assured and that even if Rubio did manage to pull a come-from-behind victory out of thin air, it's not immediately obvious -- to me, at least -- where he would go from there.

Added into this mix is the fact that Rubio is only 44 and is still widely regarded as a star within the party -- this race notwithstanding -- at the moment. Managing how and when to get out of the presidential race -- and what to do and say on your way out -- is of critical importance to how the party bigwigs and the base view Rubio going forward.

And on that matter of the "how and when," opinions are deeply divided.

"Stay in, fight hard, never quit," advised Rick Wilson, a longtime Florida Republican strategist. "The politics of some strategic concession are more damaging than a determined finish. All the missiles are already launched; the ads are airing, the mail is hitting and an early bailout ABSOLUTELY gives another 99 delegates to Trump."

Others are more skeptical that Wilson's "damn the torpedoes" approach is the right one for Rubio's future.

"With his vote share dropping like a stone, Marco needs to get out now to preserve his political options for the future, whether it is another run for president or a run for governor," said one senior Republican strategist based in Washington who spoke on the condition of anonymity to speak candidly about a sensitive subject. "Staying in will only diminish him."

"Before [Tuesday] night, I would have advised playing it out through Florida and working to deny the Sunshine delegates," said another longtime Republican adviser who has worked extensively in Florida. "But Tuesday night makes that probability seem slim – as do more recent surveys. So the smart move is to get out between the Thursday debate and the Tuesday primary, assuming there is no detectable and serious surge heading into the weekend."

The central issue in all of this for Rubio is just how much of a chance he has of knocking off Trump and depriving the billionaire of the state's 99 delegates. (Florida is a winner-take-all state, so whoever finishes first statewide, um, takes them all.) The average of polling in the state, according to Real Clear Politics, puts Trump ahead by a wide 17-point margin. But, a Washington Post-Univision poll released Thursday morning had Trump at 38 percent and Rubio at 31 percent -- a more manageable (and overcome-able) deficit.

If Rubio sees a plausible path to victory -- like a 2 in 5 chance rather than a 1 in 10 chance -- he'll almost certainly stay in the race. That's the easy calculation. The harder one is if the polling he and his campaign are seeing suggests that a blowout loss -- that's anything in the double digits -- is possible. To lose that badly on your home turf would be a stunning and very public rebuke that might take a very long time to come back from.

Although no one thinks Rubio might reconsider his decision not to run for a second Senate term -- his dismissal of the importance of the Senate during this campaign might make that close to impossible -- he is rumored to be a potential candidate for the open governor's seat in 2018. You don't want the last thing Florida voters see of you being a crushing defeat. Bad taste in the mouth and all that.

Then there is the whole question of how Rubio decides to leave the race. If it comes before Tuesday, does he endorse another candidate? (Cruz???) If he doesn't, does he make plain his views on, say, Trump?

"Do you try to blow up the Trump candidacy, and what do you do if that fails?" asked a GOP insider who has spent decades on the Florida political scene. "Do you try to steer the outcome to Ted?"

Judging from Rubio's most recent comments on the race, it seems unlikely -- although not impossible -- that he would spend his final days in the race on a kamikaze mission against Trump. "That's not something I'm entirely proud of," Rubio told "Meet the Press" host Chuck Todd during a town hall meeting Wednesday night of his decision to attack Trump at a very personal level. "My kids were embarrassed by it, and you know if I had to do it again, I wouldn't."

So, when Rubio goes, it's unlikely that will do so in a blaze of glory against Trump. But does he make a bet on Cruz's ability to, eventually, wrest the nomination from Trump -- and, in so doing, preserve his potential as a ticket mate for the senator from Texas? Or does he simply say so long and thanks for all the fish and disappear off the presidential stage, licking his wounds and preparing for either a governor's race in 2018 or another presidential race in 2020 or 2024?

What Rubio does -- and how he does it -- over the next five (or so) days will make a difference in his still-bright political future. Getting into a race is easy. Getting out of one -- the right way -- is incredibly difficult.