The Occupy movement entered a tumultuous new phase over the Jan. 28 weekend, with a violent protest by Occupy Oakland resulting in 400 arrests. Meanwhile, Occupy D.C. faces a noon Monday deadline to leave McPherson Square in downtown Washington.

Oakland, Calif., has been the scene of some of the most turbulent protests of the Occupy movement. Sunday was the most volatile yet. Protesters clashed with police, in some cases hurling rocks and bottles. A group that broke into City Hall smashed glass cases, scrawled graffiti on the walls and burned an American flag. Oakland has generally been the most radical Occupy branch, with a small minority refusing to fully renounce violence.

We're tired of one faction using Oakland as their playground, said Mayor Jean Quan, a Democrat, who has oscillated between mollifying and condemning Occupy Oakland. People in the community and people in the Occupy movement have to stop making excuses for this behavior.

The Oakland protest spurred a solidarity march in New York, with protesters chanting New York is Oakland; Oakland is New York as they moved up Fifth Avenue. The New York Times reported 12 people were arrested, mostly for disorderly conduct.

Occupy D.C. faces the prospect of a confrontation between police and protesters after the National Park Service announced  Friday it would enforce a ban on camping on federal parkland. That encompasses the Occupy D.C. encampments at McPherson Square and Freedom Plaza. A police officer stunned a protester with an electric shock on Sunday, aggravating tension that is building in anticipation of the deadline.

Many of us will be likely to defend the park with the passion anyone would show defending their home, Sam Jewler, who has been protesting at McPherson Square, told the Washington Post.

The Oakland demonstration was conceived as an attempt to take over the vacant Henry J. Kaiser Convention Center. Occupy Oakland has embraced a tactic of civil disobedience, twice shutting down the city's busy ports. Protesters warned Mayor Quan in a letter on Wednesday that they could launch an indefinite occupation of Oakland's airport, port or City Hall if they could not seize the convention center.