Donald Trump speaks during the Saturday's Republican presidential debate in Greenville, S.C. (John Bazemore/ AP)

Donald Trump's extended riff on 9/11 last weekend — "the World Trade Center came down under the reign of George W. Bush," and so on — has not merely been rejected by the mainstream right. It has been described as disqualifying, as a conspiracy theory, as something "a liberal Democrat" (per Dick Cheney) or "Michael Moore" (per Jeb Bush) might say. And many of the critics have used a potent neologism, "truther," to insist that Trump has gone beyond the bounds of sanity.

"I thought Trump really exposed himself as a truther, and I don’t think that will play real well in South Carolina," said Rep. Jeff Duncan (R-S.C.), a Ted Cruz endorser, on the radio this week.

"Watch him backtrack, lie about what he said, and go full 9/11 truther," wrote RedState's Leon Wolf.

Republican strategist Patrick Ruffini got in on it in a different, less pejorative manner:

There is some harm being done to language here. "Truther" is a word coined to describe a person who thinks something happened on 9/11 other than the story we were told. Some say the American government planned the attack — a "false flag" operation to gin up war.

There's really no evidence that Trump doubts the facts of 9/11 — that 19 hijackers affiliated with al-Qaeda managed to evade detection and take down four commercial planes, two of them destroying the World Trade Center and murdering thousands of people.

Instead, Trump is being subjected to a truther-ization that should be familiar to anyone who criticizes the Bush administration's pre-9/11 counterterrorism efforts, or pre-9/11 foreign policy more generally.

Start with Ruffini's aside that "Ron Paul went 9/11 Truther at a debate." In May 2007, then-Texas congressman Paul got only a few questions at a Republican presidential debate. Asked whether he was "out of step" with Republicans over his opposition to the Iraq War, Paul asked his own question: "Have you ever read the reasons they attacked us? They attack us because we've been over there; we've been bombing Iraq for 10 years."

Giuliani blew up at Paul. "That's an extraordinary statement, as someone who lived through the attack of September 11, that we invited the attack because we were attacking Iraq," he said.

"I believe very sincerely that the CIA is correct when they teach and talk about blowback," Paul said.

By no reasonable definition was this "trutherism," or conspiracy theory. Paul did not question the facts about the 9/11 attack itself. To the contrary: His "blowback" answer assumed that the known facts about the attack were all true.

Similarly, Trump's tantrum about the Bush administration only makes sense if he assumes that the facts of 9/11 are all true. His argument is not that Bush was behind it; it is that Bush defenders can hardly say he "kept us safe" by pretending his presidency started after 9/11. The Saturday debate was not actually Trump's deepest wade into this. Last year, on CNN, Trump flatly said that the Bush administration had ignored warnings about a plot against America.

"His brother could have made some mistakes with respect to the actual hit because they did know it was coming," Trump said. "George Tenet, the head of the CIA, told them it was coming. So they did have advanced notice.”

At the time, PolitiFact judged this claim "false," but not because the CIA had never warned of a terror threat. It had. Trump got over his skis in saying "it" — i.e., the specific 9/11 attack — "was coming." Bush had received an intelligence briefing about al-Qaeda's desire to attack within the United States, not that it would come on September 11, 2001.

In interviews since the debate, Trump has repeatedly said that he was referring to a lack of coordination between government institutions and that better "management" might have stopped the attacks. That is simply not what people who doubt the official story of 9/11 believe.

"We don’t know exactly what Donald Trump means by this," said Ted Walter, the director of strategy for Architects and Engineers for 9/11 Truth. "But I would not interpret that as him calling for a new investigation. There has been no accountability for what happened, and no one in the U.S. government has been held to answer for it. Perhaps Trump’s comments shed light on that, but I don’t think that was where he was going."