Donald Trump leaves the stage after speaking during a Super Tuesday night event in Palm Beach, Fla. (Luke Sharrett/Bloomberg)

Robert Kagan is a senior fellow at the Brookings Institution and a contributing columnist for The Post.

A mugger pulls a gun on Jack Benny and says, “Your money or your life.” Benny is silent, so the mugger says again, “Your money or your life!” Benny responds, “I’m thinking it over!”

Thus so far the collective Republican reaction to the great question of our time: If Donald Trump wins the nomination, will the party support this would-be authoritarian to inhabit the nation’s most powerful office? To watch Republicans and conservatives wrestle with this question is to understand how political parties die and how democracies give rise to authoritarian rulers.

Any doubt about Trump’s authoritarian inclinations ought to have been answered by now. Yes, it’s possible, as former Republican Senate majority leader Trent Lott suggests, that he “might wind up being the most magnanimous, inviting and generous person you could imagine.” But it is more likely that he will wind up being the person he has appeared to be throughout his campaign, only more so. The pattern of recent weeks is that the closer Trump gets to wielding the powers of the presidency, the less presidential he seems and the more he looks like the kind of strongman who brings democracies down.

He has employed threats and intimidation in attempts to silence a critical media — “If I become president, oh, do they have problems”; get a judge dismissed from a civil trial because he’s Hispanic and therefore “extremely hostile to me”; discourage private donors from giving money to opposition campaigns — “they better be careful, they have a lot to hide”; and, this week, to gain the obeisant cooperation of the speaker of the House of Representatives — “Paul Ryan . . . I’m sure I’m going to get along great with him. And if I don’t, he’s going to have to pay a big price.” Trump’s apparent fascination and, in some cases, evident admiration for Vladimir Putin, Mussolini and the Chinese perpetrators of the Tiananmen massacre would be merely strange if they did not offer a glimpse at what George F. Will has called the style of “anticonstitutional authoritarianism” by which he would be likely to govern.

Insult after insult flew during the Fox News GOP debate on March 3. Here's a look at some of the choice words rivals Marco Rubio, Ted Cruz and Donald Trump had for each other, while John Kasich stayed out of the fray. (Jenny Starrs/The Washington Post)

Those who hope a President Trump would be different, either because the job would humble him or because he would be hemmed in by our system of checks and balances, are wagering a lot on questionable suppositions. Consider that Trump is displaying these flashes of bullying authoritarianism while he is still courting us. Imagine when he no longer needs to court anyone, when he has amassed a large enough popular following to win the White House. We are supposed to believe that at that point, after a campaign in which his devoted throngs have cheered every threat and insult — against judges and newspapers and speakers of the House — he is suddenly going to become Calvin Coolidge?

Trump’s supporters obviously aren’t worried about any of this. But what about those in the Republican Party who do worry about Trump? Shouldn’t they be willing to do whatever is necessary to prevent him from winning the presidency, including voting against him in the general election, if that proves to be the only way?

Yes, there are now woefully belated efforts to block his nomination. But what if these fail, as is quite likely? Are Republican leaders prepared to take the next necessary step?

For many Republican leaders, so far the answer is no. “I wouldn’t be a very good Republican,” said Sen. Orrin Hatch (R-Utah), explaining why he couldn’t fail to support Trump in the general election, despite the risks. Some argue that a Trump presidency is worth swallowing because at least a Republican would be in the executive office, able to carry out Republican policies and make Republican decisions on critical matters such as Supreme Court nominations. Think of all the damage that will be done if Hillary Clinton and the Democrats are elected, they say.

This would be a stronger argument if Trump’s record were not one of doing whatever he needs to do at any given moment to serve his own needs. Who knows whom he would appoint to the court, and why? Maybe he would appoint someone who favored changing U.S. libel laws or had a conveniently expansive view of presidential powers.

The party’s bigger problem is that it remains enslaved by the same Manichaean mistrust and intolerance that helped give rise to Trump in the first place. And yes, the other party suffers from that ailment, too. It has displayed its own derangement syndromes, and much of what ails the U.S. political system can be laid at the doorstep of the Democrats. But at the moment the other party is not in the process of nominating a Trump. It is the Republican Party whose failings now threaten the well-being of American democracy. Can party leaders now rise above the party to save it?

Historically, authoritarians have ridden to power in democracies partly because their supporters, in the end, feared and hated their opponents more than they loved the particulars of democracy. Today, it seems, it is Clinton, and everything she supposedly stands for, who must be defeated, even if it means electing a man like Trump. As one Republican official put it, looking ahead to the general election, “The penchant to defeat Hillary Clinton will transcend any concerns about the way Trump has conducted himself.”

Really? Any concerns? You sometimes get the feeling that if Mussolini himself were about to win the nomination, Republicans would still be talking about Clinton’s email server.

This is nonsense. Republican voters and the party leaders who oppose Trump should declare now that they won’t vote for him in the general election under any circumstances. If people feel better about voting for a third-party candidacy, if one emerges, that’s fine, since any Republican vote going to a third-party candidate is a vote taken away from Trump. If more people made it clear now that they won’t ever vote for Trump, it might even help stall Trump’s drive for a majority of delegates in the coming primaries and open the way for a brokered convention. But so long as leading Republicans continue to say that, at the end of the day, they will stick with their party, right or wrong, Trump will keep rolling and the nation will remain at risk.