Sanders, unlike our current President, hasn't been encouraging political violence of any kind. But some Republicans are already trying to smear him with it.
Emma Vigeland is about two generations too young to have been around personally involved in the debates of the 1960s and early 1970s. But she has a serious and nuanced view, and seems to have a good instinct for the kind of polemics that the Republicans will use in a case like this, BREAKING: Bernie Sanders Denounces Volunteer Who Shot Congressman TYT Politics 06/14/2017:
I understand when Emma or others say "violence is never the answer." And I wouldn't criticize her for how she puts it, because she's speaking in a particular moment and trying to discourage murder, which is a good thing to discourage.
Unfortunately, in real life, "violence is never the answer" is not universally applicable. Even the small number of genuine pacifists in the United States would recognize a right of self-defense when confronted by imminent danger. Instances of sexual assault or domestic violence come immediately to mind.
The Republicans use the right of self-defense as justification for things like the "stand your ground" laws now in effect in various states now, which essentially makes it easier to people to get away with murder. Especially white people murdering black people or Latinos.
The fact that the gun lobby misuses the concept of self-defense for its own purposes doesn't make it invalid. But trying to assassinate Congresspeople and their staff on what appears in today's case with a rifle from a distance doesn't fit with any kind of sensible concept of self-defense. The shooter
One further point this brings to mind for me. Sanders never advocated violence during his campaign. But to me, the ugliest act of Hillary Clinton's campaign and then-DNC Chair Debbie Wasserman-Schultz claimed that Bernie supporters at the Nevada state caucus were throwing chairs and sending death threats to delegates. If there is any evidence for that having happened, I've yet to see it. But that was a truly irresponsible ploy.