President Trump supporters gather outside of an arena in Manchester, N.H., before Thursday evening's rally. (Spencer Platt/Getty Images)

From the floor of President Trump’s rally in Manchester, N.H., on Thursday night, an observer could see any number of red “Make America great again” hats. In every direction, the word “Trump” was visible, on T-shirts, hats, pants — even socks. Various catchphrases associated with the Trump campaign (like “build the wall”) were scattered around the room, too.

But one previously common sight was less readily apparent: The letter Q.

For more than a year, adherents of a sprawling, bizarre conspiracy theory called QAnon have sought to use Trump’s campaign rallies as vectors for spreading their beliefs. Proponents of the theory, which posits (among other things) that Trump leads an underground, international effort to uproot rampant child sex trafficking, quickly figured out that the rallies involved two useful components: Sympathetic ears and plenty of cameras. At a rally in Wilkes-Barre, Pa., last year, several QAnon supporters with whom I spoke said that they’d become aware of Q — the anonymous figure behind QAnon who claims to share inside details from the White House — by seeing references to him in the replies to Trump’s tweets. What’s a Trump campaign rally, after all, but Trump’s Twitter presence brought to life, a place for the president to be showered with favorites in the form of applause?

In the room in Manchester, though, their presence was muted. A woman in a sparkly “Q” shirt stood up and waved a Trump sign at one point. On the floor, a couple of QAnon supporters were visible, one a woman with a “Q” on the back of her shirt and another a more arcane reference: a shirt reading “Trump / 2020 / JFK Jr.” (One branch of the theory includes speculation that the late son of John F. Kennedy didn’t actually die in a plane crash and is, instead, a living Trump supporter.) Other than that, not much.

After the rally, I spoke with two QAnon supporters who independently offered an explanation for why: QAnon supporters had been asked to cover up Q signifiers or to turn their shirts inside out.

Gerald Berube, 27, was wearing a shirt with a large Q and a string of characters, “WWG1WGA” — an abbreviation for “where we go one, we go all,” a Q slogan. He explained that as he was going through security at the event he was asked by a man he identified as Secret Service to turn his shirt inside out. He said he saw two other people, whom he didn’t know, who were asked the same thing. His theory was that the request was made because “people on the left would paint us as the bad guys.”

Berube’s claim was bolstered by tweets from other Q supporters making a similar claim, as well as by John Lampiris, 53, who wore a shirt featuring a large Q as he left Trump’s speech.

“They asked me to do that,” he said, when asked if he’d been asked to turn his shirt inside out. (He instead covered it up with another shirt.) He figured that it was a function of their wanting to “control the narrative.”

But who’s the “they?” Berube’s assertion that it was the Secret Service is rejected by the Secret Service itself.

“The U.S. Secret Service did not request, or require, attendees to change their clothing at an event in New Hampshire,” the organization's director of communications, Cathy L. Milhoan, told The Post by email.

Secret Service weren’t the only people present at the entrance to the venue. Staffers for the arena were there as were a number of unidentified individuals in suits. The Trump campaign didn’t respond to requests for comment.

It is understandable that the campaign would be leery about the presence of QAnon at his rallies. It’s uncommon for political rallies to regularly be a vector for a campaign other than the candidate’s, and it’s unlikely that Trump’s team isn’t terribly enthusiastic about being associated with some of QAnon’s bizarre theories.

Trump himself, however, bears some blame for the overlap between his base and QAnon. His campaign was predicated on the idea that a nefarious cabal of elites was hoping to swing the election; he claimed even in the rally in New Hampshire that the vote in the state had been stolen from him. It’s a short path from accepting that narrative to assuming an even broader conspiracy in which Trump himself is involved.

“The permission that having a conspiracy-theorist-in-chief offers suggests that [conspiracy theorizing] can be much more explicit than it previously was,” Mark Fenster, professor of law at the University of Florida and author of “Conspiracy Theories: Secrecy and Power in American Culture,” told me when we spoke in 2017.

Luckily for the president, neither Berube nor Lampiris saw Trump as a necessary component of what QAnon offered. To Berube, that was a worldview, a request that Americans dig into claims for themselves. To Lampiris, QAnon was a lasting representation of the populism that Trump elevated in U.S. politics.

“It’s now the Trump party, the populist party, not the Republican Party,” he said. “It transcends Trump. When he’s out of office, if he gets elected or not, if it’s 2020, 24 — this populist movement transcends him.”

Maybe. But that got a lot harder in recent weeks.

For months, QAnon followers have reported that their visibility at Trump’s rallies has been stifled. The more significant recent blow is that 8chan, a website that served as the primary vector for new messages from Q (referred to as “dumps” in the vernacular), was essentially taken offline after briefly hosting an anti-immigrant screed linked to the alleged mass shooter in El Paso. Without 8chan, it’s not clear how Q can update — or how adherents can know which messages are actually from Q.

Lampiris is confident that Q will continue posting. He admitted that his support of the anonymous source could end up being wrong, but he didn't see that as particularly problematic.

“It’s sometimes nice to believe in something that’s good,” Lampiris said. “Everybody that’s decent wants to believe that good always beats evil. That light always comes after darkness. So it can also be a positive thing for people, just to believe that there are good forces trying to battle bad forces.”