Usually with those protest organizing sites anyone can post that they're organizing one, they might get a number of people indicating that they plan to attend, then on the day of they don't all show up. I recall responding to one once in the early 2000s and at the last minute receiving a message that due to low response, our event is going to join the event 15 miles away.
I'm sure a few large cities will get a sizable turnout. No shortage of fools, it seems.