Republican presidential contender Donald Trump said on Dec. 7 that he was in favor of a '"total and complete" shutdown of Muslims entering the United States. (C-SPAN)

It is happening here.

With his call for “a total and complete shutdown of Muslims entering the United States,” Donald Trump has crossed an uncrossable line of bigotry and xenophobia. The Republican front-runner presents a clearer, more present danger to U.S. interests than the supposedly threatening Muslims he seeks to exclude. He is a one-man recruiting tool for the Islamic State.

This was not Trump off the cuff, a Trump gaffe, Trump taken out of context or Trump responding ambiguously to a leading suggestion.

It was Trump being Trump, which is to say, crude, intolerant and ignorant. Yet nothing Trump has said previously comes close to this un-American suggestion.

And nothing in my experience of U.S. politics has been so sickening, has made me so embarrassed for my country. Who could have imagined that any supposedly mainstream political candidate — no less the front-runner of a major political party — would propose anything so extreme?

Republican presidential candidate Donald Trump wants to stop all Muslims from coming into the United States. Here's what he has said about Muslims since 2011. (Sarah Parnass/The Washington Post)

How would Trump enforce this? By questioning entrants about their religion? By singling out those with particular names or from particular countries? What actual terrorist would “confess” to being Muslim? What other Muslim — any Muslim, anywhere — would not be grievously offended? Are we supposed to somehow feel better that Trump’s next-day clarification allowed that U.S.-citizen Muslims could return to this country?

Indeed, given his assessment of the alleged dangers of Muslim visitors, would Trump stop at foreign Muslims? After all, he cited a poll, conducted by a right-wing, anti-Islam group, purporting to show that 25 percent of the 600 polled believe that “[v]iolence against Americans here in the United States can be justified as part of the global jihad.” And he has refused to say whether he would have interned Japanese Americans during World War II, or even whether, in retrospect, the camps violated American values.

Maybe, just maybe, Trump — after calling Mexicans rapists, questioning John McCain’s war heroism, criticizing Carly Fiorina’s looks, mocking New York Times reporter Serge Kovaleski’s disability — has finally entered self-destruction territory. His latest is not simple offensiveness — it is the marriage of offensiveness and policy.

There is some reason for hope, in the appalled reaction of most of Trump’s Republican opponents. Trump’s “habit of making offensive and outlandish statements will not bring Americans together,” said Sen. Marco Rubio (Fla.). Jeb Bush termed Trump “unhinged.” New Jersey Gov. Chris Christie said Trump’s proposal “is the kind of thing people say when they have no experience and no idea what they’re talking about.”

Others were shamefully mild. A spokesman for Ben Carson said visitors “should register and be monitored during their stay,” but that “we do not and would not advocate being selective on one’s religion.” (Except for saying earlier that a Muslim shouldn’t be president, that is.)

And Sen. Ted Cruz (Tex.), hoping to lure Trump voters if and when he craters, could only manage to choke out, “That is not my policy,” adding, “I believe the focus should focus on radical Islamic terrorism.” There’s a beacon of moral bravery — topped off by Cruz the next day, offering, “I do not believe the world needs my voice added to that chorus of [Trump] critics.”

All Republican lawmakers, party officials and candidates must immediately renounce Trump and assert that they will not support this demagogue at the top of the ticket. Failing to do so implicitly associates them with Trump’s bigotry. House Speaker Paul D. Ryan (Wis.) went halfway, saying that Trump’s proposal “is not what this party stands for. And more importantly, it’s not what this country stands for.” If so, why does Ryan say he’ll support “whoever the Republican nominee is”?

Trump speaks to a fear of Islamist terrorism that is palpable and understandable. There will always be some space in politics — and some temptation for politicians — to cater to the ugly, nativist instincts that such anxiety generates.

In European countries, these urges often find their outlet in fringe parties — or, perhaps, not so fringe. See France, where Marine Le Pen’s far-right National Front led after the first round of recent regional elections; Le Pen has called for an end to all immigration, legal and illegal.

The United States does not have a tradition of robust third parties; our extremists, of the left and right, must try to find a home within the two-party system. And when someone like Trump goes too far — when his approach, as former vice president Dick Cheney said, “goes against everything we stand for and believe in” — the parties have a responsibility, to the country as well as to themselves, to discredit the messenger and denounce his message.

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