I’m old enough to remember when Donald Trump’s refusal to declare a third-party run off-limits was enough to make him the enemy of the Republican establishment.

Now, many of those same figures are openly preparing to elect Hillary Clinton if Trump wins the nomination. Here, for example, is Weekly Standard editor-in-chief Bill Kristol this morning:

And yesterday, Politico ran a story suggesting that the Republicans might create their own third party if Trump ran. Jeff Greenfield wrote:

[I]f the operatives I talked with are right, Trump running as a Republican could well face a third-party run—from the Republicans themselves….If you want to see the most sulfurous assaults on Trump, don’t look to the editorial pages of the New York Times or the comments of MSNBC personalities; look instead to the most prominent media voices in the conservative world: National Review, The Weekly Standard, Commentary and the columns of George Will and others.

It wouldn’t be unprecedented for an establishment candidate to run third party. In 1980, for example, Rep. John Anderson (R-IL) competed in the primaries, then declared his own independent candidacy after Ronald Reagan won the nomination. In 1964, no establishment candidate ran third party, but all the major establishment Republican voices refused to back Barry Goldwater.

Would that be the right move with Trump? Only if you think that Trump is David Duke.

As Greenfield points out, in 1991 Republicans stopped Duke from winning his gubernatorial runoff:

While [Duke] proclaimed himself a Republican, he was roundly rejected by the party at every level—the outgoing GOP governor endorsed former Governor Edwin Edwards—and Duke lost overwhelmingly to Edwards. (It’s a campaign best remembered for the bumper sticker touting the ethically challenged Edwards: “Vote for the crook—it’s important.”)

But Trump isn't David Duke. Duke was an open racist, a conspiracy theorist about everything ranging from Jews controlling the Federal Reserve, and a founder of the Knights of the Ku Klux Klan. Trump says dumb things.

But that won’t stop Republican establishment figures from treating him like Duke.

At the very least, the movement to bolt the Party would be an ironic one, given the Republican Party leadership’s insistence that Tea Partiers step behind moderate candidates like John McCain and Mitt Romney in order to deny Barack Obama the White House. Those leaders tossed around supposed conservative disloyalty as an epithet.

Today, however, they’re preparing to leave if Trump wins the nomination.

Which, of course, is why Trump is winning. Which may force that inevitable break.

If so, that break has been a long time coming.