If Donald Trump becomes the Republican nominee, one of the main reasons will be that many in the conservative movement found him acceptable. And one of the main reasons that many conservatives are finding Trump acceptable is that the most influential political talk radio host in history, Rush Limbaugh, has provided his blessing.

Not his endorsement. Limbaugh takes pains to preserve neutrality between Trump and Ted Cruz, whom he describes as the obvious choice “if conservatism is the dominating factor in how you vote.”

But Limbaugh has also consistently defended Trump as a legitimate choice for those whose dominating factor is the humiliation of “the establishment.” Early in the campaign, when Trump attacked Sen. John McCain’s (R-Ariz.) status as a war hero, Limbaugh responded by praising Trump’s courage, defending him as “an embattled public figure” willing to “stand up for himself, double down and tell everybody to go to hell.” Through a long series of controversies, Limbaugh has excused Trump’s narcissism and bluster as an endearing “schtick.” Trump’s deviations from conservative orthodoxy are noted but considered secondary. “I think with the case of Trump,” argues Limbaugh, “there’s a much bigger upside than downside.”

[The decline and fall of the GOP]

The upside, in this view, is not just taking the political fight to liberalism; it is also overturning a failed and corrupt Republican political order. Limbaugh dismisses defenders of this order as fundamentally self-interested. “[Trump] has put together a coalition that’s exactly what the Republican Party says that it needs to win, and yet, look what they’re doing. They’re trying to get Trump out of the race, because they’re not in charge of it.” Opposing Trump is the work of a “cliquish, elitist club,” preserving its influence and employment prospects. This criticism is sometimes expanded to include the conservative intelligentsia. “I’m talking about the establishment,” says Limbaugh, “conservative media, the brainiacs, the think tanks, the professors.”

Republican presidential front-runner Donald Trump visited the editorial board of The Washington Post on Mar. 21. Here is audio of the full, unedited interview. (Gillian Brockell/The Washington Post)

For decades, Limbaugh set the tone of popular conservatism by arguing for ideological purity. Now, the great champion of conservatism has enabled the rise of the “least conservative Republican presidential aspirant in living memory” (in the words of Yuval Levin, editor of National Affairs). Trump is a candidate who talks more of personal rule than of limited government. A candidate who praises a single-payer health system, proposes higher taxes on the wealthy, opposes entitlement reform and advocates the systematic destruction of Ronald Reagan’s foreign policy. This is the politician Limbaugh has given the ideological hall pass of a lifetime.

Why might this concern your average conservative brainiac? First it is necessary to dismiss Limbaugh’s consistent questioning of motives. Many men and women I know who work on Capitol Hill, in conservative media or in think tanks are hardly in it for the money or job security. Criticizing their venality from 30,000 feet in his Gulfstream jet rings particularly hollow.

[George Will: Do Republicans really think Trump will make a good Supreme Court pick?]

Most in this Republican “establishment” believe they are serving a set of ideals, which includes market economics and limited government. There is no longer a Nelson Rockefeller wing of the GOP that is attempting to block the rise of the conservative movement. Leaders such as House Speaker Paul D. Ryan (Wis.) and Senate Majority Leader Mitch McConnell (Ky.) are conservative by any serious measure. But they are forced to live within the constraints of our constitutional system. They don’t have the option of inhabiting a fantasy world where entitlements such as Obamacare can be undone by the legislature alone. Such utopianism is fundamentally at odds with constitutionalism.

And many Republicans, in Washington and elsewhere, do not view civility, inclusion and tolerance as forms of weakness or compromise. In fact, they view casual misogyny, racial stereotyping and religious bigotry as moral failings, in their children and in their leaders. And they oppose — as a matter of faith or philosophy — any form of populism that has exclusion, cruelty or dehumanization at its core.

In reading Trump’s recent interview with The Post’s editorial board, what is striking is not only his shallowness (though his policy depth must be measured in microns). It is also his utter rootlessness. None of his ideas or proposals is placed in the context of ideals or ideology, Republican or otherwise. Trump possesses impulses and instincts. He does not reason from first principles. Whatever the appeal of his authoritarian populism, it does not remotely resemble conservatism (see Russell Kirk’s 10 principles, which include belief in an enduring moral order, political prudence, and restraints on power and human passion).

Populist anti-intellectualism, on the rise at least since Sarah Palin, has culminated in Trump. It is the passing of conservatism, even if Limbaugh baptizes the dead.

1 of 45 Full Screen Autoplay Close Skip Ad × Trump captures the nation’s attention on the campaign trail View Photos The Republican candidate continues to dominate the presidential contest. Caption Businessman Donald Trump officially became the Republican nominee at the party’s convention in Cleveland. Donald Trump speaks at a campaign event at Trump Doral golf course in Miami. Carlo Allegri/Reuters Buy Photo Wait 1 second to continue.

Read more from Michael Gerson’s archive, follow him on Twitter or subscribe to his updates on Facebook .