President Donald Trump's campaign released an ad last month that featured multiple supporters holding QAnon signs, a debunked conspiracy theory that claims Democrats are trying to overthrow or even kill Trump.

The ad, which has since been taken down, came weeks after the FBI determined that conspiracy theories pose a domestic terrorism threat.

The pro-Trump QAnon conspiracy centers around an anonymous individual known as "Q," who claims to have top secret security clearance and alleges that there's a worldwide conspiracy that Trump will take down.

There is no evidence that any aspect of the conspiracy theory is true, and multiple media outlets have debunked it.

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President Donald Trump's campaign released an ad in July that featured multiple Trump fans holding QAnon signs, a debunked conspiracy theory that claims Democrats are trying to overthrow or even kill Trump, just weeks after the FBI found that conspiracy theories pose a new domestic terrorism threat.

In a "Women for Trump" video posted by the campaign late last month, which was first reported by Vox, a supporter is seen holding a sign that says "Keep America Great" with a "Q" taped onto it. Later, another supporter is seen holding a "Women for Trump" sign where the O's were replaced with "Q"s. The ad has since been taken down.

The pro-Trump QAnon conspiracy theory centers around an anonymous online individual known as "Q," who claims to have top-secret security clearance. The Daily Beast reported that the figure first surfaced in October 2017 on the fringe website 4chan, before moving over to 8chan.

The conspiracy alleges, among other things, that the former special counsel Robert Mueller was appointed to investigate Hillary Clinton, Barack Obama, and other top Democrats who opposed Trump; that the so-called American "deep state" tried to shoot down Air Force One before Trump's summit in North Korea earlier this year; and that Trump is going to fix it by sending Obama, Clinton, and others to Guantanamo Bay.

There is no evidence that any aspect of the conspiracy theory is true, and it has been debunked by multiple media outlets. Still, it's not unusual to spot multiple signs promoting QAnon at Trump rallies.

Read more: Conspiracy theories pose a new domestic terrorism threat, according to a secret FBI document

In an intelligence bulletin dated May 30, 2019 that was obtained by Yahoo News, the FBI determined that "anti-government, identity based, and fringe political conspiracy theories very likely motivate some domestic extremists, wholly or in part, to commit criminal and sometimes violent activity."

The bureau went on to lay out several events over the last several years in which "perpetrators intended to kill groups identified by such theories as hostile and malevolent," or to carry out "dangerous, unlawful acts in an effort to draw attention to or expose a perceived conspiracy."

One of those events was when a Nevada man used an armored truck to block traffic on the Hoover Dam Bypass Bridge in June 2018. He was arrested after fleeing to Arizona and authorities found body armor, ammo, rifles, and a flash-bang device inside his vehicle.

Citing a technical source with direct access, the FBI said the man directly referenced the QAnon conspiracy theory after his arrest. The media also reported that he sent letters to Trump from jail that featured a QAnon slogan.

The FBI's assessment is particularly noteworthy given the uptick in not just the number of conspiracy theories but the ease with which they're spread online.

Read more: A former senior FBI official said agents are hamstrung in fighting white nationalist violence because they're 'wary of pissing off the guy in the Oval Office'

Several conspiracy theories — and the outlets that publish them — have even found their way into the White House. Trump famously pushed the baseless claim that Obama was not born in the United States.

Since he took office, the president and his allies have often suggested that he is the victim of a "deep state" conspiracy to undermine his presidency and ultimately remove him from office.

Many Trump supporters have also embraced the so-called "Spygate" conspiracy theory in recent months, which alleges, without proof, that the FBI planted a spy within the Trump camp during the election to undermine his campaign.

Trump is also cozy with Alex Jones, the founder of the far-right conspiracy website InfoWars.

Meanwhile, the right-wing media sphere, including staunch Trump ally Sean Hannity, whipped itself into a frenzy after the 2016 election when a fake news report said the Democratic National Committee was connected to the death of former DNC staffer Seth Rich.

Law enforcement authorities say Rich's murder was in fact tied to a robbery, and a Yahoo News investigation recently revealed that Russian intelligence was originally behind spreading the conspiracy theory.