As a DC Metro native I’ve been attending big events in DC and on the Mall since I was a toddler (JFK funeral).
Looking at the Breitbart time-lapse vids and some other photos, I’ll stick with my first guesstimate of maybe 200,000 to 300,000 max.
1 million seems excessive, 2 million is absurd.
There are more than 300,000 visible in that one photograph, posted earlier in the thread.
2,000,000 may be an upper-end estimate, but it is completely plausible.