Donald Trump had his worst debate performance yet Saturday night. But it wasn't because of his constant interruptions and shouting. It was because he marked himself as the conspiracy theorist candidate.

First he said President George W. Bush was to blame for letting 9/11 happen. We assume Trump meant Bush let it happen negligently rather than intentionally, but still it's impossible to accept if one asks what exactly he could have done, absent specific intelligence of the unprecedented attack that was about to take place.

Would citizens have submitted to onerous airport inspections and long lines on the basis of vague fears? Would Congress have agreed to such a thing, absent actionable info? Could Bush have grounded flights without Congress, and if so, when? How long would that have been tolerated? One day? Two?

Could Bush have persuaded Congress that the CIA should be allowed to give the FBI information it gathered on American citizens? That wasn't an easy sell even after 9/11. Imagine how well that would have gone over beforehand.

The fact is, although the concept of someone crashing a plane on purpose was known to federal officials since at least 1995, 9/11 surprised everyone. It changed the world, and everyone's expectations about what terrorists would try.

Trump then repeated the charge that Bush brought the country into war in Iraq despite knowing Saddam Hussein had no weapons of mass destruction. This ceaselessly repeated charge is and always has been disingenuous. And it is uttered by people who either don't know the facts or don't care about them.

The belief that Saddam had active WMD programs did not start with Bush. As Peter Wehner recounts in a new piece in Commentary this week, intelligence services all over the world believed it to be the case. President Clinton and Secretary of State Colin Powell believed he had them, as did many people on both sides of the debate over the war. Trump himself, who more or less advocated war with Iraq in his 2000 book, certainly believed it. (Although Trump claims to have opposed the Iraq War, there is no record of him ever taking that position prior to the invasion.)

It was later revealed that Saddam's own generals believed he had them. They were disappointed when told, just three months before the U.S. invasion, that there were none with which to repel the attack. Before he was executed, Saddam confessed that he worked hard to give the false impression that he was manufacturing and stockpiling such weapons, lest regional enemies (namely Iran) understand that he was vulnerable. His ruse was plausible — he'd run chemical and biological weapons programs before and had used such weapons in the 1980s and 1990s.

The Silberman-Robb Commission, which in 2004 investigated what had gone wrong in the invasion, reviewed the intelligence briefings that Bush had been given about Iraq, which were substantially identical to the information given to Congress. The commission's report described these classified briefings as "alarmist." By its description, they lacked even the nuance of the publicly available National Intelligence Estimate, which in 2002 had concluded that Iraq "has continued its weapons of mass destruction programs" and "if left unchecked ... probably will have a nuclear weapon during this decade." Meanwhile, the Director of Central Intelligence, first-term Clinton appointee George Tenet, described the case as a "slam dunk." Why did he do so? Because he believed it.

Most Americans now agree that the Iraq War was a terrible mistake. But shoddy work by the intelligence services does not make a liar of Bush, Clinton, or anyone else who based their actions on it.

Trump knows he gains in the polls with each of his outrages; it's what makes some people believe "he tells it like it is." But he doesn't tell it like it is. He tells it like he is clueless and doesn't care.

In the same debate, he claimed he could fix Social Security's retirement system by simply weeding out dead retirees whose checks are still being mailed every month. In a recent radio interview, he jumped on the bandwagon of those entertaining conspiracy theories that there was foul play in the death of Supreme Court Justice Antonin Scalia. This week, Trump has been circulating a comment about his rival Ted Cruz, supposedly from former Sen. Tom Coburn, R-Okla., which Coburn tells us is an "absolute fabrication." Trump also resurrected the completely false birther conspiracy that Cruz is not a U.S. citizen by virtue of his birth in Canada, and is thus ineligible to serve as president.

If GOP primary voters reward Trump's conspiracy-mongering and lies, they should be aware that general election voters are less likely do so. Every available poll suggests Hillary Clinton or Bernie Sanders would beat him if he is the Republican nominee.