GOP frontrunner Donald Trump. Thomson Reuters

Members of the Republican "establishment" are finally grappling with the likelihood that their party is about to nominate Donald Trump. But they still don't understand how they brought this phenomenon on themselves.

Here is my suggestion to them: If you want to understand how Trump invaded your party, think first about what Ben Carson's campaign, and other campaigns like it, say about your party.

It has become routine for people who obviously never ought to be president, like Herman Cain, to enjoy success in the Republican primary polls for a time and conservative fame — and speaking fees and book sales — thereafter. Sarah Palin has made a similar career without ever technically running for president, raising funds instead for a political action committee that mostly spends money on consultants, giving very little to actual Republican campaigns.

This time, it was Ben Carson who ran a "normal" scam campaign similar to the one people were expecting Trump to run. He raised a lot of money and enjoyed a brief honeymoon in the polls before collapsing under scrutiny, sold books, and made his campaign consultants wealthy, built a brand that can be monetized on the conservative speaking circuit, and compiled a fundraising list that can be rented out to other campaigns for years.

Ben Carson. REUTERS/Mike Blake

Often, when these candidates aren't running for president, they rent their mailing lists and their personas to peddlers of doomsday investment strategies and nonsense natural cures, as when Mike Huckabee endorsed a cinnamon-based natural diabetes cure. (Note: Cinnamon does not cure diabetes.) Republican insiders have tended to view these scam candidates with a mix of disdain and amusement, but not alarm.

These candidates might be taking $50 donations from old ladies on fixed incomes who really should do something better with their money, but they are ultimately pretty harmless because they always lose.

But what does it say about the Republican Party that its voters spent even a week or two seriously contemplating giving the presidency to Herman Cain? Republican insiders should have realized the appeal of scam campaigns was a symptom of a problem with the way Republican voters evaluate candidates — and that eventually, someone smarter than Herman Cain would come along and figure out how to run the scam long enough to win the nomination.

Herman Cain. Justin Sullivan/Getty Images

It's not normal for a political party to rent frontrunner status to cranks and charlatans for weeks at a time. Disastrous candidates are supposed to be blocked by validating institutions. Policy experts explain that their proposals do not add up. The media covers embarrassing incidents from their past and present. Party leaders warn that they will be embarrassing or incompetent or unelectable.

The problem is that Republicans have purposefully torn down the validating institutions. They have convinced voters that the media cannot be trusted; they have gotten them used to ignoring inconvenient facts about policy; and they have abolished standards of discourse by allowing all complaints about offensiveness to be lumped into a box called "political correctness" and ignored.

Republicans waged war on these institutions for a reason. Facts about policy can be inconvenient — a reality-based approach would find, for example, that tax cuts increase the deficit and carbon emissions cause climate change. Acknowledging the validity of complaints about racism could require some awkward conversations with racist and quasi-racist voters in the Republican coalition.

Of course, we're now seeing the unintended consequence of the destruction of those institutions and the boundaries they impose around candidate acceptability: In doing so, Republicans created a hole that Donald Trump could fly his 757 through.

Is the press reporting that some of Trump's businesses disserved customers and lost money? Well, you can't trust liberal media institutions like Fox News. Is his tax cut irresponsibly large? Don't worry, Trump will make us so rich it won't matter. Should we be concerned about his rants against Mexicans, either because they are offensive or because they will turn off voters? That sounds like something Obama would worry about.

Trump is woefully incoherent and self-contradictory on policy, and often has terrible ideas when he does get specific, but that doesn't make him much worse than average in today's Republican party. It's hard for Republican insiders to call his $10 trillion tax-cut plan absurd when Marco Rubio wants a $7 trillion one.

In addition to making it hard to attack Trump for policy unseriousness, the choice to decouple from reality has made Republican insiders less situationally aware. Who can forget 2012, when Republicans convinced themselves the polls were skewed and Mitt Romney was really leading all along? In this campaign, Republican insiders — and not a small number of reporters — failed to panic about Trump early enough in part because they bought into a repeated idea about Rubio surges that were not borne out by the polling or the voting.

Republican U.S. presidential candidate Trump gestures between rival candidates Rubio and Cruz at the U.S. Republican presidential candidates debate in Detroit Thomson Reuters

The emerging conventional wisdom is that Rubio and other establishment candidates screwed up through tactical errors — failing to take Donald Trump seriously early on, not adjusting their messages to meet the mood for populism, not putting campaign resources in the right states. There is a lot of finger pointing about who should have been doing opposition research on Trump and who should have been running attack ads against him and when.

"Party leaders, donors and other supporters of Rubio portray a political operation that continues to come up short in its message, in its attention to the fundamentals of campaigning and in its use of a promising politician," declares The Washington Post in a Rubio pre-mortem — amusingly skipping over the possibility that Rubio is losing because people simply do not want to vote for him.

It may well be true that Rubio's campaign is inept, but in a healthy political party, a savvy campaign would not have been necessary to defeat Trump. The whole reason Republican campaigns failed to take Trump seriously early on was that his unsuitability for the presidency was supposed to be self-evident: Eventually, one of the many outrageous things he said would do him in, without his opponents even having to argue against him.

Republicans will not be able to protect their party from future Trumps without redeveloping institutions that impose accountability — institutions that make reality matter, and allow the self-evident to be evident.