Warning to Republicans: beware the Ides of March.

That would be Tuesday, Mar. 15, when four crucial states — Florida, Ohio, Illinois and Missouri — will hold primaries. It’s also the first day when Republican rules allow states, if they choose, to hold winner-take-all contests. Florida, with 99 delegates, and Ohio, with 66, are doing just that. Whoever comes in first wins the whole pot.

Both states have a favorite son in the presidential race — Senator Marco Rubio in Florida and Governor John Kasich in Ohio. But the Republican frontrunner Donald Trump leads the polls in Florida and is closely competitive in Ohio. If Rubio and Kasich lose their home states, they would be finished.

Anti-Trump Republicans are investing heavily to stop Trump. Three different political action committees are expected to spend more than $10 million on anti-Trump ads in Florida.

Trump’s response: Go ahead, punks. Make my day. Trump’s spokesman called it “another desperate attempt by the out-of-touch establishment elites and dark money that control the weak politicians to maintain control of our broken and corrupt system.”

For decades, two armies have been at war over the Republican Party. The struggle goes all the way back to 1976, when Ronald Reagan challenged President Gerald Ford and nearly beat the incumbent for his own party’s nomination. It has always been the mainstream Republican establishment (Washington and Wall Street) versus the conservative counter-establishment.

The mainstream establishment is pinning its hopes on Rubio. But he seems to be sinking fast. Conservatives are rallying behind Senator Ted Cruz (R-Tex.). Cruz, the Tea Party favorite, won the straw poll at the recent Conservative Political Action Conference. Trump, meanwhile, is leading both of them.

Cruz may be able to hold on for a while. He’s winning low-turnout Republican caucuses, as he did on Saturday in Kansas and Maine. A choice that comes down to Cruz and Trump would leave mainstream Republicans in despair: The old enemy (Cruz and the Tea Party) versus the new enemy (Trump).

“We are witnessing history,” former Reagan speechwriter Peggy Noonan wrote in her the Wall Street Journal column. “Something important is ending.”

An army of outsiders is trying to take over the Republican Party. Its cause is anti-establishment populism. The Republican army is supposed to be fueled by hatred of President Barack Obama. But Trump’s army is driven by another hatred that appears to be just as intense: hatred of the Republican Party establishment that has failed to stop Obama.

Trump’s signature attitude is defiance. His supporters see voting for him as a way to defy the Republican Party establishment. “I want to see Trump go up there and do damage to the Republican Party,” one Mississippi voter told the New York Times. An Arizona voter said, “We’re going to use Donald Trump to either take over the GOP or blow it up.”

Former Massachusetts Governor Mitt Romney, the 2012 GOP presidential nominee, embodies everything Trump voters hate about the Republican establishment. Romney doesn’t have a populist bone in his body. Worse, he let Obama beat him in 2012. There was Romney last week, warning Republicans that Trump is a “fraud” and a “phony.”

Romney went so far as to insinuate that Trump is an extremist. “This is the very brand of anger,” he said, “that has led other nations into the abyss.” Germany for example?

Trump is not an ideologue. And he’s not a professional politician. He’s a businessman. His supporters believe government should be run like a business.

It’s a deeply held American belief that politics is the enemy of problem-solving. Why can’t we deal with the national debt? Too much politics. Why can’t we deal with climate change? Politics. Trump, like businessman Ross Perot before him, promises to keep politics out of government and just get things done. Everybody knows there’s no politics in business, right?

But there’s a reason government can’t be run like a business. Business is not a democracy. If business were a democracy, it would look like government: less efficient, more political. That’s why Trump has a taint of undemocratic extremism. He wants to run government like a business. With himself as boss.

The last hope of the anti-Trump forces is to prevent Trump from going to the Republican National Convention in July with the number of delegates needed to nominate him. If Trump doesn’t win a on the first ballot, we could see a brokered convention. Then maybe the anti-Trump forces could rally behind another candidate.

They’re deluding themselves. Suppose Trump goes to the convention with the largest primary vote and the largest number of delegates, even if it’s not a majority. Does anyone believe Trump would stand by and watch the party nominate a candidate who did worse than he did? Or a candidate who didn’t even run in the primaries?

The Trump army would protest that the party establishment is rigging the game and rejecting the people’s choice. That way lies pandemonium. Trump supporters would disrupt the convention and possibly walk out. It would be Chicago 1968 all over again.

Some anti-Trump Republicans are talking about splitting the party and running another GOP candidate in November if Trump becomes the party nominee. Wouldn’t that be suicidal? Wouldn’t it ensure the election of former Secretary of State Hillary Clinton, now the likely nominee?

Of course it would. But anti-Trump Republicans may be making a longer-run calculation. If Trump became president, he would destroy the Republican Party. If Clinton became president, she would unite the Republican Party — against her.

And the party would live to fight another day.