At a rough guess: 5 sections; 20 rows per section; 15 seats per row...1500 seats.
Even if he filled every one and had another 100 or so along the walls, 1600 people. 1750 max. Still dwarfed by Trump events!
...and Obama couldn’t fill that room?
I’ve been in that room. It’s one that has walls you can pull out to make it in to several smaller rooms. You could probably fit 2-3k depending on how it’s configured.