If you asked law enforcement professionals which extremist movements most threaten America, what would you expect them to say? If you expect their most common answer would be Islamic extremists, it turns out you'd be wrong — though not by much.

In a 2014 survey, the National Consortium for the Study of Terrorism and Responses to Terrorism (START) surveyed hundreds of law enforcement personnel at the state and local level, all of whom had training in intelligence gathering or counterterrorism. They were presented with a list of radical groups and asked to rate, on a scale of 1 to 4, how much they agreed that this group posed a terrorist threat to the US.

The folks at Dadaviz put together a chart of the results, as well as the results from a 2007 version of the same survey. It shows, on the left, the groups that law enforcement professionals in 2007 most viewed as terrorist threats, with the results from 2014 on the right. One of the interesting changes was for Islamic extremists, which dropped from the No. 1 to No. 2 spot — replaced by the anti-government "sovereign citizen" movement, which climbed up from No. 8:

One important caveat: The survey was released in July 2014, one month after ISIS swept northern Iraq. It's unlikely the results take into account ISIS's rise since, which means that if the survey were taken today, you might see different results.

But regardless, the findings are striking. It's possible that the Islamic extremism decline was a blip, though it makes sense given the ebbing of the "war on terrorism" after the Bush presidency. But there's no way that increase in concerns about the sovereign citizen movement is random. Clearly, something happened to alarm the law enforcement community.

Who are the sovereign citizens?

To understand what, you need to understand a little about sovereign citizens, as they're not like other anti-government extremists. Sovereign citizens believe in a weird conspiracy theory that says, essentially, that your citizenship is not real. Either the 14th Amendment or the move off the gold standard, depending on which "sovereign" you talk to, stripped Americans of their rights; all so-called citizenship rights accorded today are fake.

Sovereign citizens conclude from this that they are under no obligation to obey any laws enforced by our "illegitimate" government. They are, themselves, sovereign under true American law — and thus cannot be bound by the agents of the impostor state. Usually, their actions are limited to bizarre legal maneuvers: They'll file an overwhelming number of injunctions to avoid paying speeding tickets, file absurd liens against prosecutors' homes, or fabricate driver's licenses from fake Native American tribes.

These tactics, sometimes called "paper terrorism," hardly amount to an al-Qaeda-level threat. But the number of sovereign citizens appears to have swelled since the late 2000s as part of a general rise in anti-government sentiment. Reliable estimates are really difficult, as the movement doesn't have any formal structure, but the Southern Poverty Law Center guesses there are somewhere between 100,000 and 300,000 sovereign citizens in the US.

And occasionally, they've been violent. In 2010, a father-son duo named Jerry and Joseph Kane killed two police officers with an AK-47 during a traffic stop, and wounded two others before being killed themselves. According a 2012 Anti-Defamation League report, there's a "growing tide of sovereign citizen activity and violence across the country ... if the movement's growth is allowed to continue unchecked, further acts of violence are inevitable, putting government officials, law enforcement officers, and private citizens all at risk."

And that, perhaps, is why law enforcement officials are growing so alarmed. Sovereign citizen ideas have been around for decades, but sovereign citizens traditionally aren't violent. An increase in size coupled with high-profile violence would mark a new, and disturbing, direction for the movement — especially since their ideas incline them to target police, prosecutors, and other government agents.