By Paul Krugman – The New York Times.

So Republicans are going to nominate a candidate who talks complete nonsense on domestic policy; who believes that foreign policy can be conducted via bullying and belligerence; who cynically exploits racial and ethnic hatred for political gain.

But that was always going to happen, however the primary season turned out. The only news is that the candidate in question is probably going to be Donald Trump. Establishment Republicans denounce Mr. Trump as a fraud, which he is. But is he more fraudulent than the establishment trying to stop him? Not really.

Actually, when you look at the people making those denunciations, you have to wonder: Can they really be that lacking in self-awareness?

Donald Trump is a “con artist,” says Marco Rubio — who has promised to enact giant tax cuts, undertake a huge military buildup and balance the budget without any cuts in benefits to Americans over 55.

“There can be no evasion and no games,” thunders Paul Ryan, the speaker of the House — whose much-hyped budgets are completely reliant on “mystery meat,” that is, it claims trillions of dollars in revenue can be collected by closing unspecified tax loopholes and trillions more saved through unspecified spending cuts.

Mr. Ryan also declares that the “party of Lincoln” must “reject any group or cause that is built on bigotry.” Has he ever heard of Nixon’s “Southern strategy”; of Ronald Reagan’s invocations of welfare queens and “strapping young bucks” using food stamps; of Willie Horton?

Put it this way: There’s a reason whites in the Deep South vote something like 90 percent Republican, and it’s not their philosophical attachment to libertarian principles.

Then there’s foreign policy, where Mr. Trump is, if anything, more reasonable — or more accurately, less unreasonable — than his rivals. He’s fine with torture, but who on that side of the aisle isn’t? He’s belligerent, but unlike Mr. Rubio, he isn’t the favorite of the neoconservatives, a.k.a. the people responsible for the Iraq debacle. He’s even said what everyone knows but nobody on the right is supposed to admit, that the Bush administration deliberately misled America into that disastrous war.

Oh, and it’s Ted Cruz, not Mr. Trump, who seems eager to “carpet bomb” people, without appearing to know what that means.

In fact, you have to wonder why, exactly, the Republican establishment is really so horrified by Mr. Trump. Yes, he’s a con man, but they all are. So why is this con job different from any other?

The answer, I’d suggest, is that the establishment’s problem with Mr. Trump isn’t the con he brings; it’s the cons he disrupts.

First, there’s the con Republicans usually manage to pull off in national elections — the one where they pose as a serious, grown-up party honestly trying to grapple with America’s problems. The truth is that that party died a long time ago, that these days it’s voodoo economics and neocon fantasies all the way down. But the establishment wants to preserve the facade, which will be hard if the nominee is someone who refuses to play his part.

By the way, I predict that even if Mr. Trump is the nominee, pundits and others who claim to be thoughtful conservatives will stroke their chins and declare, after a great show of careful deliberation, that he’s the better choice given Hillary’s character flaws, or something. And self-proclaimed centrists will still find a way to claim that the sides are equally bad. But both acts will look especially strained.

Equally important, the Trump phenomenon threatens the con the G.O.P. establishment has been playing on its own base. I’m talking about the bait and switch in which white voters are induced to hate big government by dog whistles about Those People, but actual policies are all about rewarding the donor class.

What Donald Trump has done is tell the base that it doesn’t have to accept the whole package. He promises to make America white again — surely everyone knows that’s the real slogan, right? — while simultaneously promising to protect Social Security and Medicare, and hinting at (though not actually proposing) higher taxes on the rich. Outraged establishment Republicans splutter that he’s not a real conservative, but neither, it turns out, are many of their own voters.

Just to be clear, I find the prospect of a Trump administration terrifying, and so should you. But you should also be terrified by the prospect of a President Rubio, sitting in the White House with his circle of warmongers, or a President Cruz, whom one suspects would love to bring back the Spanish Inquisition.

As I see it, then, we should actually welcome Mr. Trump’s ascent. Yes, he’s a con man, but he is also effectively acting as a whistle-blower on other people’s cons. That is, believe it or not, a step forward in these weird, troubled times.