Calling Trump a racist didn't work the first 687 times but maybe...
That's because Republican primary voters don't care. The general electorate is very different, and videos like these could be used to jack up minority turnout even more. They will not see things the way Trump supporters do, obviously.
Trump is a rude loudmouth jerk, but acting like he's trying to bring back segregation or racial strife is rediculous. Good for fooling stupid people though.
True, but the nature of his campaign and some of the context from his words (eg, old NC man punching black guy) creates an environment where certain people, particularly racial minorities, will be far more open/swayed by videos like this.
It's not like Trump did nothing to encourage such videos. His campaign brought this on with its behavior and Trump's encouragement and/or tolerance of violence. When you have old white Southerners punching and kicking black people on live television, you might think it would be wise to step in and make sure it stops/never happens again. Trump did no such thing. He nurtured a reality where people could paint him as a racist, even if somewhat unfairly.