It's interesting to compare and contrast the demonstrations in Seattle the next day. A few key differences I noticed.
1) The groups were kept completely separate and not in close proximity to one another. Police vigilantly and diligently prevented left wing agitators trying to get to the Pro-Trump rally and stir up trouble.
2) Police used pepper spray and flash bombs to prevent ANTIFA agitators from engaging in their usual crap like setting fires and damaging property.
3) Pro-Trump rally attendees were escorted in and out of the venue under heavy police protection.
4) After the rally was over and a few demonstrators from both sides did directly confront each other, they ended up sharing a joint. That's not to say it wasn't heated and couldn't have easily become violent, but they managed to control themselves and I think they both felt safer with the heavy police presence. Don't get me wrong, these were not the types from either side that would have a hippie love fest and they certainly didn't, but they did manage not to escalate to physical violence.
I have zero doubt the Seattle Police would have been just as vigilant in protecting white supremacist groups as they were protecting Pro-Trump supporters. Violence just becomes a recruitment tool for both sides. We're definitely seeing a surge in ANTIFA numbers and violence, but the MSM, cable news especially, is still trying to ignore it. Print media has been catching on and reporting on it much better and in more depth.
Wapo put together a great video capturing both their numbers and tactics and it is not flattering.