One week after a double murder on a Portland MAX train horrified the city, a man riding a Blue Line MAX in East Portland started pummeling a TriMet operator who asked him to stop screaming about First Amendment rights.

The alleged assault occurred shortly after 2:15 pm this afternoon at the MAX station on East 102nd Avenue and Burnside Street. As the train approached the station, the operator asked a passenger to stop shouting, says Portland Police Bureau spokesman Sgt. Chris Burley.

"He was screaming and yelling about First Amendment rights," says Burley. "The operator of the train broadcast over the loudspeaker that he needed to quiet down."

When the train reached its stop, the operator went into the train's passenger car to ask the man to leave. The passenger physically attacked him, though accounts differ slightly on how. Police say he punched the driver. "He struck him several times," says Burley.

TriMet says the driver was pushed to the ground. Other passengers pulled the man off the driver.

TriMet spokeswoman Roberta Altstadt says the driver wasn't seriously hurt.

"The operator received minor cuts and bruises, that sort of thing, but wasn't transported for medical care," she says. "He will be fine."

The alleged assailant was arrested blocks away. Police have identified him as 23-year-old Steven Caldwell. He's been charged with fourth degree assault and three misdemeanors.

The attack was first reported by KGW-TV.

The assault comes at a raw moment for the city.

It's been one week since two men were killed trying to stop the anti-Muslim harassment of two teenage girls on a Green Line MAX train. The suspected killer, Jeremy Joseph Christian, is a white supremacist with suspected ties to right-wing extremists who have repeatedly roiled Portland with protests.

This Sunday, those "alt-right" protesters pledge to return for a rally that could mean more violence in an already tense city. Plans for counter-demonstrations are rapidly forming to disrupt the group's rally in Terry Schrunk Plaza downtown.

At the center of these far-right protests is the demand for free speech. That demand often means pushing the boundaries of unpopular and racist rhetoric in hopes of inciting a violent response from left-wing foils.

Christian, who marched with these groups in April, entered his arraignment hearing Tuesday yelling, "Free speech or die, Portland!"