Marco Rubio, Donald Trump, Ted Cruz and John Kasich stand before their lecterns at the start of the Republican Presidential Debate in Detroit on March 3. | Getty

A gentler Trump, a nothing-to-lose Rubio and a difficult decision for Cruz.

Donald Trump will once again find himself surrounded by rivals on the debate stage Thursday night, but this could well be the last time.

With wins next week in Ohio and Florida, Trump is poised to knock out Marco Rubio and John Kasich, leaving him in a head-to-head race with Ted Cruz for the Republican presidential nomination.

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That makes Republicans’ Miami encounter a last stand for Rubio and Kasich. Both insist their campaigns are about to take flight after home-state success, but the polls suggest otherwise.

Two candidates are on the brink of elimination, one is closing in on the nomination and the fourth has a difficult strategic choice to make. Here are five things to watch for in tonight’s showdown.

1. Rubio’s exit strategy

Rubio did something Wednesday that Trump rarely does. He expressed remorse. And on Thursday, he gets a chance to make amends.

Asked about a spate of attacks he lobbed against Trump — ripping him for everything from short fingers to excessive perspiration — Rubio said he would do it differently if given a second chance. “I don’t want to be that,” he said during an MSNBC town hall. “If that’s what it takes to become president of the United States, then I don’t want to be president. I don’t think that’s what it takes to be president. I know it’s not what it takes, it’s not what we want from our next president, and if I had to do it again I would have done that part differently.”

None of this means Rubio is done attacking Trump — Rubio stood by his attacks on the billionaire’s record and policies — but it does suggest that digit length and pants wetting are fully off the table.

Rubio’s regret may also be fueled in part by the attacks’ results. Voters punished him after his plunge in the mud, handing him a string of stinging losses in primaries over the past week — including a quartet of contests on Tuesday in which Rubio was not awarded a single delegate.

And there may be another motivation for Rubio’s shift in tactics: Even if Rubio can’t recover in this race, the 44-year-old may be working to protect himself in races to come. His political career has been fueled by an inspirational personal story and an aspirational brand of conservative politics, assets he’d need for a future presidential run — or to win a Florida governor’s race when the job comes open in 2018.

2. How to manufacture a miracle

Here’s where things get tricky for Rubio. He needs a miracle comeback, and he’s sworn off Trump. So what options does he have left?

Brawling Rubio tanked. Inspirational Rubio fell short. Now nothing-to-lose Rubio has only a few days to do what every other iteration failed to for months: find a strategy that topples Trump at the polls.

And he has to do more than that: Any possible hope for victory starts with winning Florida, but he’ll have to do better than that to survive until a contested national convention to have a chance at the nomination.

Even if Rubio has a banner night on Tuesday — winning Florida and scoring half the delegates in other proportional states (a feat he has yet to accomplish anywhere but Puerto Rico) — he’d still need to win more than 80 percent of remaining delegates to clinch the nomination. It’s a marginally better math equation than Kasich’s, but still an all-but-impossible task for a campaign that has shown little life since South Carolina.

His donors were to have a chance to air their grievances Thursday at a Miami summit for his top supporters. New Mexico Gov. Susana Martinez was to headline a lunch for participants, and Rubio will join them on Friday morning for a post-debate conversation. Despite the chatter about whether he’d consider dropping out ahead of Florida to avoid an embarrassing loss there — a suggestion his campaign has vehemently denied — some are concerned that quitting early would alienate the thousands of early voters who cast their ballots for Rubio.

3. Leading from behind

How does a candidate facing mathematical elimination compete on a debate stage?

If you’re John Kasich, you do exactly what you’ve been doing all along.

“The same thought process, same formula, nothing changes, just like nothing’s really changed from the day he entered the race,” said Rob Nichols, a spokesman for the Ohio governor’s campaign. “The reality is, now that it’s winnowed down to four, he gets more time to talk. He gets to talk about things of substance and accomplishment, beyond just name-calling and punch throwing.”

But that approach has also landed Kasich squarely at the back of the primary pack for months, most notably Tuesday, when he ended up in third place in Michigan — a state he once described as a must-win and where he’d predicted a late surge.

It’s all the more striking because Tuesday is the day that Kasich officially loses any chance at clinching the nomination outright. Even if the Ohio governor has the best night of his campaign — winning Ohio and blowing out rivals in a handful of other states that divide delegates proportionally — there won’t be enough delegates remaining on the calendar to land the party’s nod.

How he justifies his continued presence in the race when he’s reached a dead end could be instructive about his intentions — to somehow surpass Trump in a contested convention in July or to extract as much leverage as he can to influence the convention process, perhaps even end up on the ultimate nominee’s ticket. A spokesman said the prohibitive math doesn’t change his approach to the remaining primaries or to Thursday’s debate.

But if he has no path to a first-ballot nomination, his fight is really to ensure that Trump fails to achieve the 1,237 delegates he needs to clinch the nomination. After Ohio, Kasich has to wait six more weeks before he has a chance to help that cause: a personal Super Tuesday that includes Northeastern and industrial states that play to his brand of politics.

4. Does Cruz trust Trump’s killer instinct?

When Rubio and Trump grappled in the last debate, Cruz came out the victor, touting his record and articulating his message while others were discussing finger length and water consumption.

He could aim for a similar performance Thursday — but only if he trusts Trump to finish off Rubio for him.

Cruz wants Rubio out of the race, and he has made no secret that his recent flurry of activity in Florida isn’t about winning the state for himself; it’s about hurting Rubio in his home state. And Cruz and Rubio have a history of clashing. They’ve accused each other of dirty tricks in previous races and have largely laughed off the notion, floated by some concerned party elders, that they should form a joint ticket to take out Trump.

Still, if he thinks Trump has Florida in hand already, Cruz can ignore them both and spend his night self-promoting.

5. Is this the start of Trump’s general election campaign?

It was difficult to detect amid the bravado and hawking of Trump-brand products, but Trump made a subtle push for party unity during his victory news conference Tuesday night.

Tuesday had moments where he set aside his grievances and made warm overtures to fellow Republicans, pledging to unite his party and heaping praise on leaders he once labeled weaklings. And he appears ready to stay on that path Thursday.

He told CNN on Wednesday that he hopes Thursday’s encounter will be a “nicer, softer, lighter debate.”

If he follows through with a more inclusive demeanor that eschews his past insult-heavy strategy, it’ll be further evidence that he’s positioning himself for a general election run even as he closes in on the nomination.

But to pull that off, he’ll have to show restraint more than in the past, when the slightest provocations from his rivals led to angry tirades and attacks. Tuesday night, Trump offered an explanation: “When they’re nasty, you have to be nasty back.”