In the days since gunmen took over a federal wildlife refuge in Burns, Oregon, the anti-federal militants have accomplished little more than exhausting the patience of locals.

At the same time, they have brought renewed scrutiny to American right-wing, anti-government extremist groups -- a population whose numbers surged in the 1990s and are on the rise once again.

A tally released Monday by The Southern Poverty Law Center, which tracks extremist organizations, identified 276 anti-government militia groups in the U.S., a 37 percent jump from 2014. The militia groups are an armed subset of so-called patriot groups that "typically adhere to extreme antigovernment doctrines and subscribe to groundless conspiracy theories about the federal government," according to the law center.

Heidi Beirich, who directs the law center's Intelligence Project magazine, said the rise of the anti-government movement follows a predictable pattern of surging during a Democratic presidency and then falling under a Republican one. Extremists like the Posse Comitatus surged during Jimmy Carter's presidency in the 1970s, while Bill Clinton led the country during a time when the militia movement was involved in high-profile confrontations that included the Waco seige, Ruby Ridge and the Oklahoma City bombing.

Extreme anti-government suspicion is a characteristic that Beirich said is unique to the United States.

"This country was founded on overthrowing a tyranny," Beirich said. "This revolutionary fervor is kind of embedded in the U.S. -- this idea if you don’t like the government, you grab guns and overthrow it.”

Southern Poverty Law Center

The re-imprisonment of two ranchers convicted in 2012 of setting fire to federal land appears to be the catalyst for the occupation of Oregon's remote federal Malheur National Wildlife Refuge, which began Saturday.

The militants vowed to resist any removal efforts with force, even though the ranchers, Dwight Hammond Jr. and his son Steven, turned themselves in Monday and rejected the occupation of the federal building.

To those like Ammon Bundy, one of the extremists occupying the building, the Hammonds came to symbolize oppression of citizens by the federal government -- which owns more than half of all land in Oregon, according to the Congressional Research Service.

"Anti-govermment extremism is all over the country, but what’s unique about the West is that it’s a place where the federal government owns a lot of land," Beirich noted. "And a lot of the anti-government extremists live in rural areas. The West lends itself to this."

Beirich said groups like the one in Oregon were galvanized after a 2014 confrontation at the Bundy family ranch in Nevada between armed militants and federal law enforcement.

"The people who went to the Bundy ranch in April of 2014 were the energized members of these groups,” Beirich said. "They pointed weapons at federal law enforcement and got away with it."

Rick Bowmer/AP A members of the group occupying the Malheur National Wildlife Refuge headquarters, wears a camouflage jacket with a patch on his shoulder Monday, Jan. 4, 2016, near Burns, Ore. The group calls itself Citizens for Constitutional Freedom and has sent a "demand for redress" to local, state and federal officials.

Brian Levin, an attorney and criminologist, said the overall risk posed by anti-government groups is growing. Levin, who directs the nonpartisan Center for the Study of Hate & Extremism at California State University, said it was a "material change" that the militants in Oregon have moved from "mere rhetoric to action, and from action to forceful action."

"This is a significant milestone because we’re seeing now a coalescence of a grassroots organization, which is responding to events and trying to influence them through show of force," Levin said. "We’re seeing aggressive and criminal conduct to make this point."

The groups tend to lack central direction, sophisticated organization and recruiting networks. Some aren't groups at all, but loners or partnerships. That can make them less of an overall threat than Salafi jihadist groups like ISIS and al-Shabaab, Levin said.

Patriot groups "don’t have the organization or hierarchal power that say, ISIS does," Levin said. "Are they terrorists? As a technical matter, yes. But on the same hand, they’re not ISIS, and nor should our response to them" be the same.

Much like in the 2014 standoff at the Bundy ranch, federal officials in Oregon have thus far declined to take the bait by challenging the militants' "kill and be killed" stance.

Levin, who described himself as third-generation law enforcement, said the "less is more" approach to handling the militants will avoid opportunity for martyrdom or further notoriety.

"When things go south, the first question is always, 'Why didn’t you wait?'" Levin said. "A court order is still valid, and can be executed at a time and place of the government’s convenience. And no one gets killed. And we haven’t given these extremists fodder for their own recruitment efforts."

While a threat exists as long as the militants remain armed, Levin noted federal officials can afford to give the occupants room, since they effectively "put themselves in their own jail" by holing up in a remote and empty building with few snacks.

"Do you want to eat frozen Spam over a half-lit fire in a desolate tundra? Knock yourself out," Levin said. "It’s not like they occupied a resort in Maui.”

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