Is Joe Scarborough having his Colonel Nicholson moment?

That’s what I wondered Monday morning as I watched the host of MSNBC’s “Morning Joe” insist that Donald Trump’s inability and unwillingness to simply and plainly denounce the Ku Klux Klan in a Sunday CNN interview was “disqualifying.”

For those who might not have seen “The Bridge on the River Kwai,” it’s partly the story of British Lt. Col. Nicholson, played by Alec Guinness. Nicholson, a prisoner of war held by the Japanese, convinces himself that he and his men should help his captors build a strategically invaluable bridge over the Kwai River. Nicholson thinks that if he shows the Japanese what good British discipline is all about, he will win some kind of moral victory. Of course, if they finish the railway bridge, the Japanese military will win an actual victory.

Only at the last minute — spoiler alert — does Nicholson realize the error of his ways. “My God, what have I done?” he says with his last breaths as he falls on the TNT plunger, destroying the very bridge he built just seconds before a Japanese train goes over it.

Nothing so dramatic transpired on “Morning Joe,” where Scarborough and co-host Mika Brzezinski have been among Trump’s most valuable boosters for nearly a year. And will likely remain that way. Indeed, it may be too late to stop the Trump train anyway.

But it would be nice to hear “My God, what have I done?” from a lot of people. A rich mixture of resentment (both misplaced and well-earned), incompetence, wishful thinking, greed and celebrity worship has led us to where we are: An intellectually and ideologically unqualified, and often unhinged, demagogue is poised to become the Republican nominee for president.

For months, GOP pooh-bahs, cable personalities (including some friends and colleagues of mine at Fox News), talk radio hosts and politicians stood by and watched — or cheered — as Trump built his populist cult of personality almost unopposed. Now that Trump has a personal relationship, as it were, with his followers, he can do no wrong.

Trump famously joked that he could shoot someone on Fifth Avenue and not lose his support. That remains to be seen, but he can play rhetorical footsie with the KKK, reveal that he thinks judges “sign bills,” subscribe to vile “truther” explanations of 9/11 and the Iraq War, embrace the health-care mandate, traffic in reprehensible sectarian tribalism and vow to weaken the First Amendment so he can exact vengeance on journalists who don’t kowtow to his Brobdingnagian ego — yet not shake loose his fans.

That “success” has bred more success, as politicians jump on board the train. New Jersey Gov. Chris Christie set a torch to his integrity by endorsing a man who stands against nearly everything Christie once claimed to believe, Christie has confirmed all the darker aspects of his reputation as a cynical, self-interested, spiteful bully.

Many decent and sincere Republicans, in and out of the Republican leadership, have been operating on the assumption that Trump will fade and that the gravest threat is a third-party run by the dean of Trump University. There was a time when that concern was defensible. But once it became clear that he was favored to win the nomination outright, Republicans should have realized that a third-party run was more like a best-case scenario.

Better the GOP do battle with a know-nothing bigot (and lose the presidency) than become the party of know-nothing bigots (and still lose the presidency).

That’s why I embrace the Twitter hashtag #NeverTrump, initiated by conservative talk show host Erick Erickson. For too long, Trump has benefited from the assumption that the non-Trump faction of the party will be “reasonable” and support the nominee. Such thinking paves the road to power for demagogues.

Trump says he gets along with everybody and will unify the country, even as he suggests that an inconvenient judge is biased because he’s Latino, vows to ban all Muslims from the country, insists his Central Intelligence Agency will torture people, and boasts that he will declare war on disloyal journalists.

When your opponent is that unreasonable, the reasonable response is not surrender.

I don’t know whether Trump will win the nomination or the presidency. But I am fairly certain that if he does, a great many people will one day say, “My God, what have I done?”

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