It's not like Trump actually went there because he wanted to win over voters. He just wanted to make it on the news, and in a sort of childish move, he wanted to get back at Bernie for saying that he could take Trump supporters (that was the whole point of going to Burlington instead of going after the republicans with whom he's actively running against).

There was nothing real about what he was doing, so he was in no way a threat (he didn't even book a venue to host all that many people because he didn't care about that, he just wanted to hand out a lot of tickets and pretend like he was going to get a big showing, it's all showmanship, nothing authenitc). I feel like it would have been easier if people just walked out instead of humoring him for so long with a protest or by listening to his speech. I'm sure he'd spin it into something like "I was so convincing we finished early" or something, but meh. It's not like it was Hillary or Rubio, in which case the coordinated protesting would have actually been necessary and important.

And Trump supporters have disrupted Bernie's town halls before. Bernie is very much about respectful discourse. Unlike how Trump supporters have conducted themselves in the past, the Trump protester at a Bernie town hall wasn't beat up, he didn't have any racial slurs thrown at him, he left with his coat, and his signs nor any other possession of his were ripped up or destroyed. There's a pretty big difference in the amount of class between the two candidates' supporters. And in accordance with the level of class and respect we expect from Bernie supporters, they conducted themselves peacefully and well.