The Republican Party’s immune system — which once fought off David Duke and Pat Buchanan with relative ease — is completely failing.

Decades of serving their base a toxic blend of white-identity politics and ridiculous promises — spiced with a paranoia that instructs them not to trust anyone who doesn’t tell them exactly what they want to hear — has left the right-wing army of older, angrier, whiter men vulnerable to an interloping con artist with a powerful sense of how to get inside his marks’ brains. And because Donald Trump tells the GOP base exactly what they want to hear, every attempt to signal his danger to the the Republican Party — and the nation — sounds like a “nattering nabob of negativism.”

The Trump virus arrives at the worst possible time for the GOP elite. On the whole, conservatism is on the rise, controlling not only both houses of Congress but more state legislatures than at any time since before the Great Depression. And with the American public rarely willing to give one party more than three consecutive terms in the White House, they have a real chance to elect a president who could set the course of the Supreme Court for decades.

But the death of Antonin Scalia, combined with the surge of the most unpopular major presidential candidate ever, has only underlined that the party’s commitment to destroying norms in the name of revanchism is blowing up at exactly the wrong time.

“Playing base politics — tolerating nativism, birtherism, and promising obstruction at every turn — could cost Republicans the presidency and threaten control of the Senate,” David Axelrod wrote.

And if Trump continues to repulse women, he could even threaten a House majority that has been insulated from practically all political reality by gerrymandering.

It’s far too late, but Republicans are attempting to marshall their resources to deny Trump the nomination on the first ballot, opening the process up on the floor of their national convention as the whole world watches them self-destruct. Many elites have decided that losing with Ted Cruz might finally silence the Tea Party without the division that a Trump nomination would unleash.

Here’s why the GOP will mostly give up the suicidal urge to deny Trump the nomination, and will end up backing him in November.

1. There won’t be an acceptable replacement.
   Who should the party turn to if it successfully dislodges Trump, who has won more delegates than all his opponents combined? Senator Ted Cruz is the walking embodiment of the GOP base’s worst instincts gone wild: an anti-intellectual Ivy League snob who believes there is a secret majority of Americans who want to elect a guy who would ban all abortion and all background checks for guns — though only 10-20 percent back these extreme views. But it’s not policy that makes him unacceptable to GOP elites — it’s his tendency to torch other Republicans and march the party’s dead-enders into the abyss. Gov. John Kasich is a conventional Republican running George H.W. Bush’s 1988 campaign for president in 2016. He plays moderate on TV but has waged a one-man war on reproductive rights and starved small-town Ohio by slashing taxes for corporations. Kasich sounds perfect for this GOP, but he accepted Obamacare’s Medicaid expansion, which basically makes him a double agent. House Speaker Paul Ryan could step in as a GOP savior again — and shows every sign of wanting to do so this year. But anyone who turns on Trump becomes the embodiment of the evil establishment, a role Ryan has somehow avoided after decades of embodying the Republican establishment. If Ryan were to step in, he would be the leader of a minority party that has basically told one-third of its supporters that the party would rather burn it all down than nominate their choice, Trump.
2. Bet against the GOP being able to unite.
   FiveThirtyEight has laid out a strategy for how Cruz and Kasich could team up to deny Trump the delegates he’d need to cinch the nomination. And it might have worked, had the party leadership tried it last January. The safest bet in 2016 is against the GOP demonstrating any ability to coordinate resources against Trump. And there’s a reason the GOP hasn’t been able to rise up and unite to take on this bigoted demagogue…
3. Trump is very popular among the party’s base and pretty much a conventional Republican.
   Birtherism is a mainstream belief in the Republican Party. Trump is about as popular at this point in the nomination process as Mitt Romney was in 2012. And Trump’s beliefs — besides some bluster about trade and earned benefits like Social Security — are boilerplate Republican. After all, John McCain won the nomination in 2008 on “Build the danged fence.” Trump is a climate science denier who opposes Wall Street reform. And his tax cuts would be perhaps the biggest giveaway to the rich… ever. He alienates exactly the voters the GOP needs to win over, and aggressively so. But so does the standard GOP platform. And what do issues matter? Today’s GOP has one unifying core belief: oppose Obama, belligerently. And who does that better than Donald Trump?
4. They hate Democrats more.
   Some Republicans will not be able to cast a ballot for Trump based on his willingness to rile dumb hate and his proud ignorance of the nascent sort of fascism he threatens. They’ll turn to a #NeverTrump candidate, perhaps the Libertarian party’s nominee. But it’s not likely they’ll back a genuine third-party candidate for one simple reason: They’ll be running against a Clinton or a Democratic Socialist. That will be more than enough to unite the Republican Party.
5. Trump has given the loyalty pledge that matters most.
   This hasn’t gotten a ton of attention, but Trump has taken what may be an unprecedented move in the history of American politics. He’s already named judges he’d appoint to the Supreme Court and is allowing the Heritage Foundation consult on a final list of 10 “conservative approved” nominees, all of whom would certainly be against voting rights, reproductive rights and the huge advances in LGBTQ rights made in the last eight years. But even more important to conservative donors, these Justices would continue the decades-long effort to undo the New Deal via the courts. With our campaign finance system, Affirmative Action and the Fourth Amendment already gutted, the Court can focus on destroying what’s left of the government that preserves the middle class — public labor unions, Social Security and federal regulations on everything from carbon emissions to the minimum wage. If Trump represents a chance to continue this Long Con, they’ll take him over allowing Clinton or Sanders to fill up to four vacancies.

Ultimately, the quickest way to unite the Republican party is to elect Hillary Clinton or any other Democrat in the general election, as anti-Trump Republican strategist Rick Wilson points out.

And what’s a better path to that than nominating Donald Trump?

Photo: Republican U.S. presidential candidate Donald Trump looks to the cameras at the back of the arena during a rally at Clemson University in Pendleton, South Carolina, in this February 10, 2016 file photo.  REUTERS/Jonathan Ernst/Files