In the hours after the Capitol was overrun on Jan. 6, a theory quickly emerged in conservative media: This wasn’t us. It was them.

The “them” was antifa, a loose-knit movement of sometimes violent activists focused on combating perceived fascism and racism. For months, President Donald Trump had been promoting the idea that antifa posed a dangerous, rampant, terroristic threat to the country. It was convenient for Trump, positing a shadowy left-wing group that demanded the response of a strong law enforcement hand. This was Trump’s reelection message, that he would hold antifa in check.

Antifa didn’t actually pose the threat that Trump suggested. The Justice Department under the leadership of William P. Barr had increased its focus on the movement but never found much evidence to substantiate Trump’s concern. The bigger threat, as the Department of Homeland Security made clear last year, was right-wing extremism, particularly white nationalist groups.

But the idea that antifa was a catalyst for unrest took hold among Trump supporters. So when unrest erupted at the Capitol that day, antifa predictably got the blame. Those storming the Capitol may have been wearing Trump gear, sure — but it was somehow antifa that was leading the charge.

Some Trump allies have speculated that antifa was responsible for inciting violence and storming the U.S. Capitol on Jan. 6. No evidence supports this claim. (Adriana Usero/The Washington Post)

That claim gained traction after the Washington Times reported that a facial recognition company had linked several of those photographed in the Capitol to antifa. That report quickly made it to Fox News and to the House floor, where Rep. Matt Gaetz (R-Fla.) elevated the theory. Unfortunately for Gaetz and Fox, though, the report was entirely incorrect and was ultimately rescinded. The storming of the Capitol wasn’t by antifa activists. It was, as it seemed, by supporters of Trump.

Yet, in a poll conducted last month by the American Enterprise Institute, half of Republicans said they thought that it was mostly or completely accurate to say that antifa “was mostly responsible for the violence that happened in the riots at the US Capitol.” Overall, 3 in 10 Americans said that statement was at least mostly accurate.

That was one of four political theories presented in the poll. A majority of Republicans also said that they thought unelected officials had been trying to undermine Trump’s presidency, a view that 29 percent of Americans hold. A contrast worth noting: Republicans were much more likely to say that the antifa theory was at least mostly accurate than they were to describe as accurate the theory underpinning the QAnon extremist ideology, focused on child sex trafficking.

The most commonly held theory among Democrats — a theory accepted as at least mostly true by nearly 9 in 10 Democrats — was that Trump had encouraged his supporters to break into the Capitol. That’s not accurate, either, but there is more evidence that Trump prompted the violence at the Capitol than that antifa did. This, after all, is the focal point of the impeachment trial that is underway in the Senate.

It is always easier to see your opponents as wrongdoers than your allies. A parent will always assume that it is their child’s friend who suggested doing the prohibited thing, not their beloved progeny. This effect was probably manifested after Jan. 6: A movement that had focused intensely on presenting itself as dedicated to law enforcement would naturally find it difficult to accept that some of its members took a different approach. So, maybe it was antifa’s fault?

This isn’t theoretical.

“That wasn’t Trump people. That’s been a hoax from day one,” Michigan state Senate Majority Leader Mike Shirkey (R) said of the riot last week. He added that it “was all staged.” He later apologized for his remarks — but was caught on an open mic admitting that he still held those views.

This is a senior elected official in a large state, embracing the idea that what happened at the Capitol wasn’t what happened at the Capitol. Despite the lack of any evidence of antifa involvement and despite repeated examples of riot participants touting their allegiance to Trump, it’s easier to assume that one’s own side is innocent.

Sometimes, it isn’t.