The calculus is that more black riots against police or ginned up racism in general will unite the black vote for Hillary and turn out all of the Leftist mush brained voters, particularly the Bernie supporters. Not everybody agrees with that analysis and argue that the backlash against the riots will actually turn out more Trump voters than will gained by the Democrats with this violence.
That’s how I see it. Fence-sitters will break for Trump with more of this nonsense. It might depress Trump’s black support as the community does what it does and coalesces, both out of identity and in many cases fear - imagine being a black Trump supporter in this environment. However, every other group - especially whites - will gravitate towards law and order and a ‘change’ candidate. Who the hell wants this as normal besides the braindead or vile?