What Boston celebrates as Patriots' Day has been morphed by many into a militia rally incorporating guns, Waco, and Oklahoma City. John Avlon on a fringe holiday growing larger each year.

Today, there will be a five-hour rally held on the Washington Mall in support of the Second Amendment. Organizers emphasize that the odd, non-weekend date for the march was chosen to commemorate the 235th anniversary of the Battle of Lexington and Concord, celebrated as Patriots' Day in Massachusetts and Maine.

But in our overheated and sometimes hate-fueled political environment, April 19th has emerged as a "Hatriot" holiday for some anti-government activists and militia groups. Specifically, today also marks the 15th anniversary of the Oklahoma City bombing of the Murrah Federal Building by Timothy McVeigh, which killed 168 innocent men, women, and children. McVeigh, in turn, was motivated by what he saw as the federal government's unlawful 1993 attack on David Koresh's Branch Davidian compound in Waco, Texas, on—you guessed it—April 19th.

A planned rally today in Oklahoma City was rescheduled only after popular outcry.

Last April 19th, the Oath Keepers announced their formation at Lexington Green, with founder Stewart Rhodes declaring, "you need to be alert and aware of how close we are to having our constitutional republic destroyed!" The group of current and former armed services and law-enforcement officers offers its supporters a list of "10 orders we will not obey" including: "orders to disarm the American people"; "impose martial law"; "invade and subjugate any state that asserts its sovereignty" and "any order to blockade American cities, thus turning them into giant concentration camps." Rhodes will be among the featured speakers today on Washington Mall.

Satellite "Second Amendment" rallies will be held this year in states like Alaska, California, and Louisiana. Separately, "articles of freedom" alleging systemic violations of the Constitution will be presented by smaller groups of activists at all 50 state capitals. Across the Potomac from D.C., an armed Second Amendment rally will be held by a group called "Restore the Constitution" in Ft. Hunt National Park, featuring some speakers from militia groups, like Three Percenter founder Mike Vanderboegh, who wrote on his blog, "It may be our last chance to convince ["enemies of the Founders' Republic"] without violence that we are done backing up… When it is done, when we have come, made our point, and left, the message will be indelible—tyranny stops here, or else." A planned rally today in Oklahoma City was rescheduled only after popular outcry.

Organizers claim the selection of April 19th is entirely coincidental—an assertion rejected by Kari Watkins, the executive director at the Oklahoma City National Memorial and Museum. "It's not a coincidence," she tells me, "They weren't doing this before Waco and Oklahoma City and in the last few years it's gained momentum. April 19th was a date specifically chosen by McVeigh and (co-conspirator Terry) Nichols as the anniversary of Waco… And if it is a coincidence, they should look around and see that it's a day that many innocent people lost lives because people did not take responsibility for their actions… In Oklahoma City, we lost a lot of lives because of the militia and because of extremism."

• John Avlon: Paranoia on Patriot’s Day As the Southern Poverty Law Center has documented, the United States saw a threefold increase in the number of militia groups during the first year of the Obama administration alone. But Timothy McVeigh's onetime defense lawyer, Jeralyn E. Merritt, cautions against making connections between today's militia movements and McVeigh, telling me "I don't think there will be a repeat based on the same events or factors that influenced McVeigh. He was pretty unique."

A Washington Times article from 1996 illustrates the date's resonance among militia members even before the Oklahoma City bombing. Forthrightly titled "Militias call April 19 'day of concern,' list events well before Oklahoma City," it quoted Militia of Montana founder John Trochman as saying "It's a date marking a reign of terror in various countries at various times." In addition to the historical events mentioned previously, April 19th is also the date of the Warsaw Ghetto Uprising against the occupying Nazis , the execution of a white supremacist named Richard Snell in Arkansas, and the date of an initial incursion at Ruby Ridge, Idaho, home of another patron saint of the fringe, Randy Weaver. It also the date when, in 1933, the United States went off the gold standard—a decision still considered controversial by "End the Fed" groups.

The rhetoric used by some promoters and speakers in advance of Monday's rallies has a decidedly militant tone. Take an article by Skip Coryell, a founder of the Second Amendment March, recently written for the conservative journal Human Events titled "Rattling the Second Amendment Saber."

"My question to everyone reading this article is this: "For you, as an individual, when do you draw your saber? When do you say "Yes, I am willing to rise up and overthrow an oppressive, totalitarian government?" Is it when the government takes away your private business? Is it when the government rigs elections? Is it when the government imposes martial law? Is it when the government takes away your firearms? Now, don't get me wrong. I'm not advocating the immediate use of force against the government. It isn't time, and hopefully that time will never come. But one thing is certain: "Now is the time to rattle your sabers." If not now, then when?... So long as our elected officials believe we will rise up and overthrow them under certain conditions, then they will not allow those conditions to occur. Their jobs and their very lives depend on it."

Another article, this time from the St. Louis Gun Rights Examiner titled "April 19th—Liberty's Show of Force" features this photo.

The article also makes passing reference to a quote by onetime John Birch Society President and conservative Georgia Democrat Congressman Larry McDonald: "We have four boxes with which to defend our freedom: the soap box, the ballot box, the jury box, and the cartridge box"—remarking "we haven't quite exhausted the first three boxes yet."

For all the evocation of history, it is important to note that the groups sponsoring these rallies are newly created. Ironically, gun laws have actually been loosened in recent years, with the Supreme Court's welcome rejection of Washington D.C.'s gun ban and President Obama's signing of a law that allows guns to be carried into national parks—legislation that makes the armed Ft. Hunt protest possible. In fact, over the past two decades, the number of states with concealed carry permits has increased from nine to 37.

But forced seizure of guns is still used as a fright-wing talking point by figures like Judge Roy Moore in his remarks at the Nashville National Tea Party Convention. We've heard these appeals since at least the 1960s, when the "patriotic resistance" militia group the Minutemen pumped up followers with news of an alleged plot "to confiscate all private firearms by the end of 1965."

Civic activism and fidelity to the Constitution is to be commended, but exaggerated fears are unhelpful because it runs the risk of engaging in incitement. Standing up for the Second Amendment is an honorable action, but its integrity can be compromised by focusing constitutional rallies on a date sullied in more recent history by a self-styled patriot who committed the most deadly act of domestic terrorism in American history.

In a speech to the Center for American Progress, Bill Clinton spoke of the lessons of Oklahoma City in today's political climate, citing the rise of "Hatriots" and cautioning that "the words we use really do matter… in this vast echo chamber… they fall on the serious and the delirious alike." It was a message seconded by the Oklahoma City National Memorial and Museum's executive eirector, Kari Watkins: "We can get to a middle ground but we can't do that with the extreme left or right—we've got to live in the middle…. We have just about knocked ourselves off that axis and we are in a very dangerous position in terms of the mood of the country."

John Avlon's new book Wingnuts: How the Lunatic Fringe is Hijacking America is available now by Beast Books both on the Web and in paperback. He is also the author of Independent Nation: How Centrists Can Change American Politics. Previously, he served as chief speechwriter for New York City Mayor Rudy Giuliani and was a columnist and associate editor for The New York Sun.