In 1872, the Democrats were in such disarray (taking the wrong line on the Civil War will have that effect) that they backed a lifelong Republican, publishing tycoon Horace Greeley, for president. Greeley was trounced. Four years later, the Democrats reverted to traditional Democrat Samuel Tilden, who won the popular vote but lost the election.

In 1896 and 1900, the Democrats nominated prairie populist and easy-money man William Jennings Bryan. But in 1904, having lost back-to-back elections, they chose stolid New York judge Alton Parker, a sound money supporter.

In 1964, the Republicans bucked their long history of nominating moderate establishment figures and selected Barry Goldwater, who flaunted his “extremism” (in the defense of liberty) and was quoted as suggesting that we “lob one [a bomb] into the men’s room at the Kremlin.” The resulting Democratic landslide was so devastating that many questioned whether the GOP would survive it. Yet four years later, Republicans won White House through Richard Nixon, one of the prior moderate nominees.

What will happen if Donald Trump is the GOP nominee this year (likely) and loses by a clear-cut margin to Hillary Clinton in November (also likely)? No one can say for sure. But the most likely outcome is that Republican voters will learn from the defeat and nominate a true Republican candidate — someone on the spectrum that runs from Paul Ryan to Ted Cruz — in 2020.

Losing stinks, which is why political parties normally react decisively to the experience. Think not just of the examples cited above, but also of Jimmy Carter following George McGovern and Bill Clinton following Michael Dukakis. Think, for that matter, of Donald Trump following Mitt Romney.

But suppose conservatives run a third party candidate in this year’s election. The suggestion has gained currency. For example, Bill Kristol says that if the GOP nominates Trump, he will work actively to put forward an “independent Republican” ticket. Kristol calls this “a one-time, emergency adjustment to the unfortunate circumstance (if it happens) of a Trump nomination.”

Unfortunately, this one-time adjustment would likely have long-term consequences. Most notably, it would probably stymie the normal corrective process that occurs after a party’s nominee goes down in flames.

If Trump loses in a race involving an independent Republican, those who backed him will be able to shift the blame for the defeat to those who backed a third candidate. The “stab in the back” will challenge (and perhaps replace) the “foolish (to put it mildly) joy ride” as the prevailing narrative of the 2016 adventure.

Instead of backing away and hoping that folks forget their role in the Trump fiasco, his leading backers will re-fight the battle of 2016. Even if they don’t prevail in 2020, they might well seek vengeance by dragging down a mainstream Republican nominee.

A third party conservative candidate in 2016 might also have a devastating effect on Republican congressional candidates this year. These candidates will have to decide whether to back Trump or the third candidate. Whatever their decision, they will alienate a large portion of potential supporters. That’s a big price to exact just to make a gesture of disgust at Donald Trump.

But the larger point is the one David Frum makes: “When people bolt their party, the party changes behind them.” Frum backs up this assertion by discussing the third party candidacies of Theodore Roosevelt, George Wallace, and Ross Perot.

Bill Kristol is a brilliant analyst. But history suggests that it’s naive to view a third-party candidacy as “a one-time, emergency adjustment.”

If conservatives bolt in 2016, they will (in Frum’s words) “leave the instrumentalities of the GOP in the hands of people who were willing to work with Trump, and whose interest post-Trump-defeat will be in adapting his legacy to the future rather than jettisoning it.” If they don’t bolt, they will be well-placed to pick up the pieces in 2020.

This is not to say that anti-Trump conservatives should vote for Donald Trump. The presumption, I think, should be in favor of voting for the Republican nominee. However, the ultimate decision is one that conservatives must make for themselves as a matter of conscience. Some will vote for Trump; some will write in another name; some just won’t vote. (I can’t imagine a true conservative voting for Hillary Clinton.)

My argument is simply that the anti-Trump forces shouldn’t go the third-party route. Our politics may resemble “the end of days,” but the end is not at hand. If Trump’s hostile takeover occurs, our focus must be on reversing it in 2020. A third-party would be counterproductive to that end.