The last four contenders for the Republican nomination for president will meet Thursday in Miami for the 12th debate of the campaign, and the three chasing front-runner Donald Trump increasingly need a gift from heaven to win a majority before the convention.

After winning three of four states up for grabs on Tuesday, Trump has a healthy but not insurmountable lead over Sen. Ted Cruz. The debate, to be aired on CNN at 8:30 p.m., will be the last chance to influence voters in the all-important state of Florida.

Here is what each man needs to do.

Donald Trump — Act presidential.
The real estate mogul has clawed his way to the top of the once-crowded field with a take-no-prisoners and spare-no-sacred-cows style that endeared him voters fed up with the politics of usual.

The intense fire Trump has taken from his opponents and Establishment figures who normally rally around the front-runner at this point in the primary season has not stopped him from winning. But it has taken a toll: His negatives are on the rise and he has not yet won a majority of the vote in the primaries and caucuses held so far.

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Rather than answering every trivial attack and returning every insult with one of his own, he would be smart to act like he already is the nominee — short answers to his opponents followed by substantive attacks on Democrat Hillary Clinton. Despite his front-runner status, he has received just a handful of endorsements from party leaders. A steady debate performance could change that.

Eschewing the Establishment has benefited him so far, but he should welcome its support now — as long as voters are assured that it is on his terms.

Ted Cruz — Unite the anti-Trump vote.
Cruz has run an effective campaign, raising gobs of cash while positioning himself as an outsider who refuses to go along with the “D.C. cartel.” But he didn’t count on Trump poaching much of his base. Now, he finds himself with a steep, uphill challenge.

Attaining a delegate majority is difficult to impossible now. Cruz’s only shot is building a coalition of anti-Trump voters and winning enough states to overtake him in the delegate lead before the Republican National Convention. With Sen. Marco Rubio’s campaign running on fumes and Gov. John Kasich looking like a regional candidate, attacking either at the debate might be counterproductive.

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Instead, he should press the case that he is a consistent conservative who is better trusted than the sometimes-erratic Trump. Cruz needs to stay above board — limiting his critique of Trump to policy — while convincing Rubio and Kasich supporters that he is the only viable alternative.

Marco Rubio — Play to Florida.
The freshman senator followed up a disappointing performance on Saturday with a disastrous Tuesday. With voters abandoning him across the country, he is down to a one-state strategy — win Florida or go home. Everything Rubio says at the debate needs to be geared toward reminding Florida Republicans why they fell in love with him in 2010.

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There is evidence that his below-the-belt personal attacks helped rough up Trump — but also inflicted damage on himself. He should lay off the personal attacks and espouse the optimism he preached earlier in the campaign. Rubio will not win the nomination even if he carries Florida, but it would at least give him bargaining chips if there is a contested convention and preserve his future in politics.

Then again, maybe Rubio should use the debate to announce he is dropping out of the race in order to increase his chance of becoming Trump’s running mate.

John Kasich — Show some fight.
Kasich has the opposite problem of Rubio. His Mr. Nice Guy routine has taken him as far as he can go. But you can’t take down the candidates ahead of you without giving voters a compelling reason.

At the last debate, Kasich passed on an opportunity to challenge Trump’s praise of Russian President Vladimir Putin — although he made the same argument in a TV ad. It does not mean that he has to slash and burn, but he does need to point out where Trump is wrong — and not just remind voters of his own record in Congress and as governor.