As the cameras rolled on President Trump's campaign rally for GOP Rep. Ron DeSantis in Florida on Tuesday night, a peculiar sign appeared in view."We are Q."Journalists at the event noted multiple attendees carrying signs and wearing T-shirts emblazoned with the name "QAnon."The shirts and signs are references to a conspiracy theory growing increasingly popular among those on the far-right — and a conspiracy theory about which the White House fielded a question from the media on Wednesday.What is QAnon?The conspiracy theory centers on a mysterious and anonymous online figure — "Q." According to The Daily Beast, "Q" began posting on anonymous Internet message boards in October 2017. The person or persons behind the "Q" persona claim to possess a top-level security clearance and evidence of a worldwide criminal conspiracy.What's the conspiracy theory?It goes like this: Special counsel Robert Mueller isn't actually investigating Trump and his 2016 campaign for their possible ties to Russia, and he's not really looking into Russian interference in the 2016 presidential election.Rather, Mueller was appointed by Trump to investigate Hillary Clinton, Barack Obama and other top Democrats, like former Clinton campaign chairman John Podesta. According to posts written by "Q" — dubbed "breadcrumbs" by the theory's followers — even Sen. John McCain, R-Ariz., is a target of Mueller's so-called investigation.What are these foes of Trump being "investigated" for? There are numerous accusations floating around the QAnon world. Some suggest Clinton and Obama are in cahoots with Russian President Vladimir Putin. Others suggest they, along with Hollywood figures and other world leaders, are participants in a global pedophile ring."Q" suggests all these figures are secretly wearing location-tracking ankle monitors, so their whereabouts can be monitored at all times, and that they'll all be sent to prison very soon in an event the theory's followers call "the storm."That's a reference to Trump's remarks last year, where he warned of "the calm before the storm" during a meeting with military leaders. (The military is also involved in the QAnon theory — according to "Q," the military persuaded Trump to run for president in order to clean up the vast criminal network.)"Q" has dropped "breadcrumbs" about coming events in the supposed investigation on a regular basis. The hints reference current political events, including the release of the Justice Department's Office of the Inspector General report in June.It should be noted that no part of the QAnon conspiracy theory has proved to be true, and multiple media outlets have debunked the theory's allegations.Who believes in the conspiracy theory?For a while, QAnon posts were mostly limited to anonymous Internet message boards, like 4chan and 8chan. But over the past year, "Q" has gained a host of new believers and followers. A popular YouTube video explaining QAnon has racked up nearly 200,000 views, and according to NBC News, a mobile phone application related to the conspiracy theory climbed near the top of the Apple App Store rankings earlier this year."Q" also counts several celebrities as followers and fans. Roseanne Barr has frequently tweeted about QAnon and has expressed a desire to meet "Q." And in June, the sitcom star took to Twitter to share a phrase common among QAnon supporters — "wwg1wga," short for "where we go one, we go all."Former Boston Red Sox pitcher Curt Schilling has also tweeted about the conspiracy theory and has shared QAnon videos on his Facebook page, according to The Daily Beast.Why does it matter?QAnon may seem on its face like a fringe Internet conspiracy theory, but its explosion in popularity has led to several real-world incidents.In April, a group of QAnon believers took to the streets in Washington, D.C., in support of "Q" and demanding answers from the Justice Department.And in June, a man driving an armored vehicle and carrying two firearms shut down a highway near the Hoover Dam while holding a sign reading "Release the OIG report."That appeared to be a reference to the Justice Department's Office of the Inspector General report that criticized the actions of former FBI Director James Comey for his handling of the Hillary Clinton email investigation. "Q" has hinted to followers on multiple occasions that Trump possesses a second IG report that would detail the criminal activities undertaken by Democrats.The man, Matthew Wright, was arrested after the incident and now faces terrorism charges. Last month, it was revealed that Wright penned letters to Trump and other government officials from jail bearing the "where we go one, we go all" slogan.Even Michael Avenatti, the lawyer representing adult film actress Stormy Daniels, made an appearance in a series of QAnon posts earlier this week, which included images of his office building followed by an image of a man reportedly standing outside Avenatti's office. "Q" later posted that a "message" had been sent to Avenatti.In a tweet Wednesday, Avenatti appeared to respond, writing: "The more conspiracy theorists attack me, the more confident I become. It shows they see me as a significant threat to Mr. Trump and his continuation in office."And following Trump's rally in Florida, QAnon made its way into the White House briefing room Wednesday, when a reporter asked White House press secretary Sarah Sanders if Trump "encouraged the support" of rallygoers wearing "Q" shirts."The president condemns and denounces any group that would incite violence against another individual and certainly doesn't support groups that would promote that type of behavior," Sanders said.QAnon isn't the first conspiracy theory to make the jump from the Internet to the real world. In December 2016, a man fired a rifle inside Washington, D.C.'s Comet Ping Pong pizzeria, citing the baseless "Pizzagate" conspiracy theory that maintains that the restaurant is the center of a child sex ring involving top Democrats, including Clinton and Podesta.The "Pizzagate" conspiracy theory originated on fringe Internet sites before emerging in the mainstream. With the ever-increasing appearances of "Q"-branded gear at Trump rallies, QAnon may be following the same path. Copyright 2018 NPR. To see more, visit http://www.npr.org/.