Mark Potok, a senior fellow with the Southern Poverty Law Center, said his organization tracked an "astronomical" growth in the number of anti-government militia and so-called patriot groups last year.
"There's a lot of populist rage out there," Potok told TPM. "Demonizing propaganda and conspiracy theories have been pushed into the political mainstream, often by politicians or other well known public figures."
The result has been a rise in the number of radical organizations. Last year, the number of patriot and militia groups swelled to 1,274 from the previous year's high of 824.
The organization detailed those findings as part of its annual report on American extremism, which was published on the SPLC website earlier in the day. The report also revealed the number of hate groups in the US, including racist and anti-gay organizations, had remained relatively steady, ticking up just slightly last year from 1002 to 1018.
Potok said the rise in the anti-government groups could be traced back to three major factors.
The first is that the racial demographics of the United States are changing quickly, with minorities on track to outnumber whites in the near future. That's symbolized, Potok said, with the election of Barack Obama, the nation's first non-white president.
The second thing fueling the growth is the financial meltdown of 2008. Not only did a lot of people blame the federal government for the collapse, Potok said, but they also faulted it for the response.
"The government favored the wealthy," he said. "Who'd they go in and save? Well they saved the mortgage bankers and the auto executives. And what really did the common man get? That, I think, is the factor out there."
Finally, the growth has taken place as conspiracy theories have gone mainstream. The theories are invariably false, but Potok said they get often get pushed by politicians and other opportunists anyway.
One popular conspiracy theory, he noted, was the idea that Mexico is planning to reconquer parts of the US Southwest by sending masses of illegal immigrants north across the border. Another theory holds that the federal government plans to disarm Americans and begin putting them into concentration camps.
While the SPLC has been criticized for putting relatively mainstream groups on its list in the past, Potok maintained that those groups that make it into the annual report somehow broke from the standard political rhetoric.
"Opposition to the government is as American as apple pie," he said. "We don't criticize or list groups for opposing this policy or that administration. The reason we list them, the reason we watch them, is that they are eaten up with conspiracy theories that are absolutely false and in some cases propel people to go out and blow up buildings and kill people."
However, while there are now more than 1,000 anti-government groups on the SPLC's list, Potok said most of them will never carry out an attack or do anything criminal.
"That said," he added, "relative to the size of the groups, the patriot movement has produced a huge amount of attempted domestic terrorism and other violence."