Feds sounded alarm on Antifa in 2016

The FBI and Department of Homeland Security have been warning state and local officials of violence coming from far-left anti-fascist ("antifa") groups for at least a year, including the potential of violence between those on the far right and the far left, per a new report.

"Department of Homeland Security formally classified [antifa] activities as 'domestic terrorist violence,'" according to confidential documents obtained by Politico's Josh Meyer. "These antifa guys were showing up with weapons, shields and bike helmets and just beating the s*** out of people," a senior law official told Politico.

Why it matters: "Both the racists and a segment of violent antifa counter-protestors are amped for battle in an escalating arms race, where police departments are outmaneuvered, resulting in increasingly violent dangerous confrontations," former New York City police officer Brian Levin told Politico.

The backdrop:

We published a summary of far-right extremist groups a couple weeks ago. Now we're also looking at four extremist groups on the far left.

Note: Most of the far-left organizations that have protested and counter-protested in Berkeley, Durham and Charlottesville in the past few weeks do not classify as "hate groups." They are not to be equated with groups like neo-Nazis and the KKK, which target people based on ethnicity, but they do represent a growing trend of left-wing groups whose members do not always shy away from violence.

The groups:

1. AntiFa has become more visibly active since Trump's election, but the movement as a whole has remained relatively secretive. Until recently, they were most well-known for their violent protests of alt-right leader Milo Yiannopoulos at UC Berkeley. They often wear black masks and commit vandalism. Go deeper with this piece from the Atlantic on the rise of the violent Left.
2. Redneck Revolt does not claim to be liberal, but supports most left-wing social causes. The group opposes white supremacy and hopes "to incite a movement amongst white working people that works toward the total liberation of all working people," according to their website. They are pro-guns, anti-racist, anti-capitalism and anti-Trump. Members of Redneck Revolt network showed up at Trump's speech in Phoenix last week armed to protect those protesting against Trump from Trump supporters and any law enforcement who might oppose them, according to their blog.
3. SURJ (Showing Up for Racial Justice) is an anti-racist group primarily led by white people, which works alongside multicultural leaders and organizations to counter white supremacist groups. SURJ believes that "none of us can be free until we end white supremacy," according to their website. While they aim to be instructive and inviting so that others will join forces with them, they also "organize to create tension and target people in power." SURJ led the protests in Berkeley last week. Although their protestors were encouraged not to be violent, many were trained in self-defense and held pastel painted, wooden shields, according to LA Times.
4. Anti-Racist Action, founded in 1988, is an anti-racist, anti-sexist, anti-homophobic, anti-discrimination group, which wants "a free classless society," according to their website. They are known to chase down and attack members of hate groups, including white supremacists and neo-Nazis, which they refer to as "boneheads," according to SPLC.