Stewart Rhodes does not seem like an extremist. He is a graduate of Yale Law School and a former U.S. Army paratrooper and congressional staffer. He is not at all secretive.

In February he was sitting at a table at the annual Conservative Political Action Conference (CPAC) at a fancy downtown hotel in Washington, handing out fliers and selling T-shirts for his organization, the Oath Keepers. Rhodes says he has 6,000 dues-paying members, active and retired police and military, who promise never to take orders to disarm U.S. citizens or herd them into concentration camps. Rhodes told a Newsweek reporter, "We're not a militia." Oath Keepers do not run around the woods on the weekend shooting weapons or threatening the violent overthrow of the government. Their oath is to uphold the Constitution and defend the American people from dictatorship.

But by conjuring up the specter of revolution or counterrevolution is Rhodes adding to the threat of real violence? Oath Keepers are "a particularly worrisome example of the 'patriot' revival," according to Mark Potok of the Southern Poverty Law Center (SPLC), which monitors hate speech and extremist organizations. "Patriot" groups described by the SPLC as outfits "that see the federal government as part of a plot to impose 'one-world government' on liberty-loving Americans" are "roaring back" after years out of the limelight, according to Potok. Notorious in the aftermath of the Oklahoma City bombing in 1995, the patriot groups seemed to fade away under the shadow of 9/11, but hard times and the nation's first African-American president seem to have brought about a revival from 149 groups in 2008 to 512 (127 of them militias) in 2009, according to the SPLC.

It is easy to exaggerate the numbers of these groups or the threat they pose, especially if you are an organization, like the SPLC, dedicated to exposing such things. Extremist outfits have come and gone over the years. With their preening and prancing about in Nazi garb or white robes, skinheads and white supremacists are often more about showing off than committing acts of violence. Law-enforcement experts worry more about "lone wolves," disturbed loners with military training, like Timothy McVeigh, the Oklahoma City bomber, than they do about loudmouth militia groups. But the feds and local authorities will be watching closely on April 19, when the Oath Keepers mark their first anniversary and join a Second Amendment March on Washington to celebrate the right to bear arms. The Oath Keepers say they are commemorating the first shots of the Revolutionary War fired at Lexington and Concord on April 19, 1775, but April 19 is also the anniversary of the end of the FBI siege at Waco, Texas, in 1993, as well as the 1995 Oklahoma City bombing.

This is a season, or perhaps an era, when politics seem more intense than usual, and the domestic extremist threat seems more real. Partisan disputes are rarely pretty, but lately they have taken a particularly ugly, menacing turn. Last week the FBI arrested individuals for making death threats against House Speaker Nancy Pelosi and Sen. Patty Murray of Washington for their votes on health-care reform. A series of -expletive-strewn voice-mail messages left for Senator Murray were particularly creepy: "You're gonna have a target on your back for the rest of your life," the caller warned. "How long do you think you can hide?"

Senate Sergeant at Arms Terrance W. Gainer said last week that serious threats to members of Congress had nearly tripled, from 15 in the last three months of 2009 to 42 in the first quarter of 2010, with most of them coming in March during the height of the health-care debate. Some of the calls and e-mails were "very vicious" and included threats to members' homes and families. "You had people saying, 'I'm going to get your kids, I'm going to get your wife,'E" says Gainer. "It was very disturbing to members."

After the health-reform vote, a tea-party activist in Lynchburg, Va., posted an address for Rep. Tom Perriello on his blog and encouraged readers to "drop by" and express their anger over Perriello's vote for the bill. The blogger got the address wrong. Perriello's brother returned home that day to find that someone had cut the line to a propane-gas tank behind his home. The fact that haters are sometimes incompetent renders them only marginally less frightening. Some threats come from people who are truly unhinged. Federal authorities have charged a man with multiple -- personality disorder with threatening in a YouTube video to kill Rep. Eric Cantor; the suspect is not competent to stand trial.

Economic distress and social change make for fear, and fear makes for anger, now and always. Night riders terrorized the defenseless after the Civil War. During the Great Depression, two demagogues in particular whipped up conspiracy theories against Jewish bankers and the rich elites to arouse angry mass movements. Huey Long, governor of Louisiana, later a U.S. senator who wanted to soak the rich, and Father Charles Coughlin, an anti-Semitic Catholic priest whose radio show reached 40 million people, seemed a political threat to FDR, until Long was assassinated and Coughlin became increasingly unhinged.

"There was a lot of hatred in the 1930s," says Alan Brinkley, the Columbia University historian and expert on populist movements. But the current surge of fear and loathing toward Obama is "scary," he says. "There's a big dose of race behind the real crazies, the ones who take their guns to public meetings. I can't see this happening if McCain were president, or (any) white male." (Secret Service spokespeople reported spikes in threats against Obama after his election and inauguration, but they've also said the president generally receives about the same number of threats as did Presidents Bill Clinton and George W. Bush. They've declined to comment on whether there's been a spike in threats related to health-care reform.)

Fear of "the other" has long fueled hate crimes, from the torture and lynchings by the Ku Klux Klan beginning in the late 1800s, to the violence of the 1950s and '60s, to the virulent anti -- immigrant groups today. In 2008 the Census Bureau announced that whites will make up only half the U.S. population in 2050. "That was a big deal," says the SPLC's Potok. In recent years white-power groups mushroomed and the Klan reversed declining membership.

The Internet has made it easy to express hatred, and may act as a kind of safety valve. But the Internet can also abet twisted minds with vitriol and practical tips, like how to make a bomb.

Middle-aged guys sitting around their basements fantasizing are one thing; addled war veterans with weapons training are another. Timothy McVeigh was a Gulf War veteran who read white-supremacist literature and the sort of books that predict a takeover by one-world government agents flying black helicopters. He has, or had, some potential heirs apparent in a recently indicted group called the Hutaree, a Michigan-, Indiana-, and Ohio-based militia. According to the Hutaree Web site, the group ranked its followers with weird sci-fi titles like "Radok" and "Arkon." The Hutaree militiamen speculate that the Antichrist is Javier Solana, a former NATO secretary-general and senior official of the European Union. The evidence? "There is a virtual media blackout on this man," writes John Reynolds, author of a screed on Solana and the Antichrist on the Hutaree Web site. "I see Jacques Chirac and Silvio Burlusconi (sic), Tony Blair, and Prince Charles on the TV all of the time, yet not a word one regarding Solana. Why not?" ("Mr. Solana has now retired and is an elderly private gentleman. This is quite insane," says a spokesman for the European Union's

The rambling rants of the Hutaree might seem funny, in a sick sort of way, but they are far from harmless. The FBI busted nine members last month for allegedly plotting to trigger an "uprising" against the government by assassinating a local police officer and then ambushing colleagues who attended the funeral by blowing up improvised explosive devices. They may have had some professional instruction: one of the men in the group, Michael Meeks, is a Persian Gulf War veteran who served four years in the Marines and was a decorated rifle expert, according to Marine Corps records. Another member, Kristopher Sickles, is an Army vet (discharged "under other than honorable conditions," according to prosecutors). William Swor, the lawyer for Hutaree leader David Brian Stone, says there is no evidence the group was doing anything other than exercising its First Amendment rights.

The Internet offers a dark social network for militiamen and real soldiers. A July 2008 FBI intelligence report by the bureau's counterterrorism division warned that white-supremacist leaders were encouraging followers to "infiltrate the military as 'ghost skins' in order to recruit and receive training for the benefit of the extremist movement." (The report said the hate-group leaders were especially interested in planting moles without any documented history with neo-Nazi groups or "overt racist insignia such as tattoos" so they could more easily slip by military recruiters. The FBI identified 203 people with confirmed or claimed military service who were active in extremist groups. On the NewSaxon.org Web site for white supremacists, a blogger called "shadowman" posted a photo of a U.S. Army enlisted man in camouflage carrying a weapon with the boast "i am a professional killer ... a soldier born of war."

The Defense Department has long had a "zero tolerance" policy for membership in extremist groups, but last November the Pentagon quietly tightened its regulations governing such activity, a Pentagon official confirmed to Newsweek. Not only are service members barred from "active participation" in such groups, they also may not "actively advocate supremacist doctrine, ideology, or causes," according to a copy of the Pentagon regulation.

It is hard to know how much such grim fantasies are stirred by the steady stream of conspiracy theories pushed by talk-radio hosts. Rush Limbaugh talks about the Democrats planning to "kill you" with health-care reform and suggests (agreeing with black Muslim minister Louis Farrakhan, of all people) that it "seems perfectly within the realm of reality" that the H1N1 vaccine was "developed to kill people." Like many talk-show hosts, he uses martial language to rouse the faithful: "The enemy camp is the White House right now," he says. Former Alaska governor turned media star Sarah Palin posted on her Facebook page a list of House Democrats who voted for health-care reform with crosshairs aimed at their home districts, while tweeting to her followers, "Don't Retreat, Instead reload!" She strongly denied any intent to incite violence. Other conservative talkers insist their foes are preparing violent attacks on them. Glenn Beck of Fox News is the master purveyor of this particular brand of sly paranoia. He suggests that he will be the victim of violence. "I'd better start wearing a (bulletproof) vest" to guard against White House attacks, he says, and warns that the Democrats will sic goons on him to break his kneecaps. Some talk-show hosts see the risk of going too far. Bill O'Reilly, the top-rated talker on Fox News, interviewed Stewart Rhodes of the Oath Keepers in February and treated him coolly. After the interview O'Reilly said to his audience, "We have a system to uphold the Constitution. It is called the judicial branch. The Supreme Court. The Oath Keepers are not the system." Wise words, but it's a sign of disturbing times that O'Reilly felt required to say them.

With Michael Isikoff, Mark Hosenball, Katie Connolly, and Daniel Stone in Washington