These were not random acts by individuals. The was a coordinated nation-wide assault on political freedom. Republican offices all over the country were attacked before the last election. The AFL-CIO made available to the Democrats thousands of its members to disrupt Republican rallies and commit acts of violence and vandalism. Without thuggery, dirty tricks and wholesale voter fraud, the Democrats can not win a national election.
At the core of most liberals is a streak of nihilism if not outright disrespect for property. The further left they are, the more anti-social and violent they are. Ideas, especially conservative ideas, that cannot be rebutted logically have to be smashed. The reaction of these leftists is the reaction of barbarians... which most far-leftists are only inches from being.