Trump lies all the time, of course. He lies about big things, like the patriotism of American Muslims. He lies about medium sized things, like his knowledge of the Mike Tyson rape case. And he lies about tiny, absurd stuff, as when he pretends to date famous women.

The media, when not just airing his speeches unfiltered, has done a decent job of calling out these individual lies. That’s why it’s all the more perplexing how great American news organizations have allowed a flat lie about the most important American policy decision in decades ooze its way into fact.

This has happened in plain view, as when Anderson Cooper let this slip by unremarked during the March 29 debate: “I was against the war in Iraq. OK?”

It happens when Trump talks to interviewers who know a thing or two about the subject, as when the Washington Post editorial board let his claim pass unremarked, and changed the subject to the size of his hands.

And it happens in passing, as in a recent Times piece that has Trump “reminding his audience that he had opposed the Iraq War.”