"These people are bad people who want to do harm to our country."
An oft repeated sentence which Trump uses to describe anyone who opposes him. This plants the seed that anyone who opposes Trump is a "real and present danger" (of some unspecified sort) who must be stopped by any means necessary.
https://www.rawstory.com/2016/03/fck...y-in-st-louis/
I think the likelihood of someone being seriously injured or even killed at a Trump event grows every day. If Trump loses either the nomination or the presidency, that becomes a virtual certainty.