At a big, classy town hall event in Rochester, New Hampshire, on Thursday evening, Donald Trump fielded a question from an unidentified man, who announced, “We have a problem in this country. It’s called Muslims. You know our current president is one. You know he’s not even an American. … Anyway we have training camps growing where they want to kill us. That’s my question: When can we get rid of them?”

Without specifying which part of the man’s diatribe he meant to address, Trump responded "We're going to be looking at a lot of different things. You know, a lot of people are saying that and a lot of people are saying that bad things are happening. We're going to be looking at that and many other things."

Trump is being rightly pilloried for not dressing down the questioner, including by Republican operatives, who are happily forwarding along the unflattering news clips that followed.

There’s no sense in giving Trump a pass on this, but it’s worth keeping in mind that this isn’t a Trump problem. It’s a politician problem, and in particular it’s a Republican politician problem. The Republican interest in Trump’s dishonorable conduct is deeply selective.

Anyone who’s watched C-SPAN call-in shows can sympathize with people put into Trump’s predicament. Campaigns, and especially campaigns, draw out the most agitated voters in the country, in the same way a political call-in line self-selects for people with things they need to get off their chests.

But these outbursts spill over into racist conspiracy theories frequently enough that the politicians really ought to have pat reprimands at the ready. They can't really get a pass for placating racists and xenophobes. And Trump isn’t even close to the only politician who fails this test, though he may be the first politician who posed it to other candidates.

Just this past March, former Senator Rick Santorum, who has since joined the presidential race, spoke at the South Carolina National Security Action Summit, and fielded a question from a woman who was alarmed that President Obama’s plan to destroy the city of Charleston with a nuclear weapon had to be thwarted by a military officer.

Why is the Congress rolling over and letting this communist dictator destroy my country? Y'all know what he is, and I know what he is. I want him out of the White House. He's not a citizen. He could have been removed a long time ago. Larry Klayman's got the judge to say that the executive amnesty is illegal. Everything he does is illegal. He's trying to destroy the United States. The Congress knows this. What kind of games is the Congress of the United States playing with the citizens of the United States? Y'all need to work for us, not the lobbyists that pay your salaries. Get on board, let's stop all of this, let's save America. What's going to stop—Senator Santorum, where do we go from here? Ted told me I've got to wait until the next election. I don't the country will be around for the next election. Obama tried to blow up a nuke in Charleston a few months ago, and the three admirals and generals—he's totally destroyed our military, he's fired all the generals and all the admirals who said they wouldn't fire on the American people.

To the extent that Santorum took offense at all it was at the implication that, as a former Senator, he bore any responsibility for Obama's communist takeover.

Literally two days ago, Donald Trump played the part of conspiracy-minded provocateur on the CNN debate stage, when Jake Tapper raised the issue of his anti-vaccine activism.

Autism has become an epidemic. Twenty-five years ago, 35 years ago, you look at the statistics, not even close. It has gotten totally out of control. I am totally in favor of vaccines. But I want smaller doses over a longer period of time… . Same exact amount, but you take this little beautiful baby, and you pump—I mean, it looks just like it's meant for a horse, not for a child. And we've had so many instances, people that work for me. Just the other day, two years old, two-and-a-half years old, a child, a beautiful child went to have the vaccine, and came back, and a week later got a tremendous fever, got very, very sick, now is autistic.

Among the 10 other candidates on the stage were two doctors—Ben Carson and Rand Paul—both of whom had an opportunity to condemn Trump and call his remarks dangerous. Both declined.

In October 2008, Senator John McCain, who was then the Republican party’s presidential nominee, famously quieted a woman at a rally who had read all about how Obama is “an Arab” (not that there’s anything wrong with that).

"No, ma'am,” McCain said after reclaiming the mic. “He's a decent family man, citizen that I just happen to have disagreements with on fundamental issues and that's what this campaign's all about. He's not [an Arab]."

The crowd booed and McCain went on to lose the election. The only reason anyone remembers the altercation is because we expect Republican politicians to behave the way Trump did.