Because Antifa is their personal enforcement army.
Their old personal enforcement army, the KKK, isn’t what it used to be.
Antifa is a division in the Marxist army in America. BLM and ghetto thugs/gangbangers are also components of the Marxist army.
The Marxist movement is bigger than the Democrat Party. The Democrat Party is just one branch.
The Democrats are controlled by the Marxists. But so is academia (including K-12), most of the media and entertainment, much of the government, even churches to some degree (like the UMC and those parts of the Catholic Church that are loyal to Pope Frank).
Even corporate America is under significant Marxist influence to the extent that it is on the Woke bandwagon.
Easy.
More mayhem justifies more government population control.