President Donald Trump on Monday urged Portland to call in the National Guard to help quell mob violence in the city.

“Portland, which is out of control, should finally, after almost 3 months, bring in the National Guard,” Trump wrote on Twitter.

Rioters on Sunday attacked a Portland Police Association building and set it on fire. They also threw commercial-grade fireworks at the officers who gathered to disperse the crowd.  Sixteen people were arrested during the riot.

The president specifically criticized Portland Mayor Ted Wheeler and Oregon governor Kate Brown, both Democrats.

“The Mayor and Governor are putting people’s lives at risk. They will be held responsible,” Trump wrote. “The Guard is ready to act immediately.”

The president has directed federal law officials to protect a federal courthouse in Portland, which was the site of several riots in recent weeks, but the mobs have moved on to other targets.

“The Courthouse is secured by Homeland!” Trump wrote, referring to the Department of Homeland Security.

On Friday, Trump singled out Wheeler who warned protesters throwing fire at occupied buildings that they were “attempting to commit murder.”

“That’s come a long way; he’s come a long way when he made that statement,” Trump said.