"In November, shortly after the presidential election, peaceful anti-Trump demonstrations were disrupted when anarchists smashed windows, ripped out electrical power boxes and spray-painted buildings downtown" 

The mayor's inability or willful unwillingness to protect any and all who choose to protest or demonstrate peacefully in the past has led to this situation. Allowing the left wing nuts to attack others with impunity has now led to the right wing nuts to believe that they can respond in kind. Believe it or not there is something to the whole 'law and order' mantra.