Seriously, who didn't see this coming?
Donald Trump has already mused about establishing a central database for tracking Muslims in America.
He has repeatedly, and falsely, claimed that Muslims in New Jersey celebrated the 9/11 attacks even while the dust was still settling on lower Manhattan.
He's called Mexicans criminals and rapists.
And that's just in the few months since he began his campaign for the U.S. presidency.
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Prior to that you'll remember his indefatigable enthusiasm for the wing-nut "birther" theory that suggested President Barack Obama was actually born in Africa not America.
The record, then, is clear: Trump has proved impossible to embarrass, utterly shameless and apparently willing to say anything.
So why wouldn't he call for a ban on all Muslims travelling to the U.S.?
The effect of his remarks on Monday was exactly what he seems to have intended. Rival Ted Cruz, who was about to take a bow for topping Trump in an Iowa poll, got shoved aside — "Trumped" as it were — to make room at the centre of the media hysteria gamely known as the national conversation.
Never mind that the conversation among many serious people has now turned to whether Trump's views are un-American.
Party leaders are taking unprecedented steps to distance themselves from Trump, and Republican Senator Lindsey Graham called him "a race-baiting, xenophobic, religious bigot."
Since that's Trump's own party speaking, you can imagine what Democrats are saying.
A different America
Outside the world of professional politics, it's even worse. There has been earnest public debate in the last few weeks about whether Trump is a fascist. A fascist!
'They're getting in, they need to be stopped.' - Trump rally attendee Deborah Moore
The respected conservative columnist Ross Douthat raised that question in the New York Times, decided Trump wasn't, and then changed his mind after Monday's news.
Another conservative, Wall Street Journal columnist Bret Stephens, tweeted that Trump's openness to a Muslim database is "fascism, plain and simple."
I have personally interviewed self-described fascists who say that Trump is a voice for their ideals.
The very idea that sensible people are giving serious thought to whether the front-runner for the Republican presidential nomination is a fascist is astonishing all on its own.
But it's totally fine with Trump because he's speaking to a different America.
'They need to go'
There was no hand-wringing at Trump's South Carolina rally on Monday night, for instance.
When it came to the Muslim travel ban, it was two thumbs up from those waiting to hear him speak.
"I'm worried about America, worried about our safety. They're getting in, they need to be stopped," said one attendee, Deborah Moore, on CNN.
"I don't want 'em here," said another, Ed Campbell. "Who knows what they're going to bring into this country, bombs, ISIS or what? They need to go."
For those people, mostly white and middle aged, Trump seems like a common sense answer to their anxieties about the world outside America.
Inside their world, he appears as the only candidate willing to speak truth to power.
Republicans must act
But that's what worries the many Republicans who see Trump as a threat. It's not just that a big part of their base wants him as their nominee; it's that those people might not vote at all unless he's their nominee.
And so Republicans have mostly pussy-footed around Trump, taking only tentative little jabs, usually in self-defence, ever wary of provoking his base.
Surely that can stop now.
Trump is a stain on the Republican Party brand that will spread further if it's not cleaned up fast. So the party needs to get busy.
They can begin at next week's candidates' debate on CNN.
If what Trump said about Muslims means anything it's that the rest of the field can finally start taking him on.
The first step is for two or three candidates to make Trump a target and establish themselves as truly sensible alternatives. This means going beyond saying, as some wishfully have, that "he won't be the nominee," to saying "he should not be the nominee, and if he is I won't support him."
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The next step will be tougher for some to swallow. There are too many candidates in the race and some need to get out.
Anyone can name a half a dozen or more no-hopers whose tiny pockets of support will eventually consolidate behind a stronger candidate anyway.
Waiting only prolongs the current agony. They should go now. The fact is Trump's poll numbers — between 20 to 30 per cent — only look good because the field is so wide.
The remaining 70 to 80 per cent represents most of the party, but is divided into too many slivers.
Who knows where "Republicans for George Pataki", or for Rand Paul, or even Jeb!, might go if let loose, but it's time to find out.
It's a reasonable guess that they won't go to Trump. His candidacy has become unsustainable.