Who Are the Rioters?

There have been riots at Trump rallies. I have an important question: Who are the rioters? The most plausible groups don't overlap much:

1. Illegal aliens and their relatives.
2. Sanders supporters.
3. Black Lives Matter.
4. Trade unions trying to elect Trump.

The rioters are burning American flags and chanting “America was never great.” This sounds like any of the first three groups and may be even be done by the fourth group as part of a literally false-flag operation. In particular, this protester doesn't look Mexican.