The movie wasn’t made for the political junkies, like us, who have watched the hearings, read the analyses of the events of that night, etc. This film is intended to reach the Average Joe or Joanne who is only vaguely aware of what happened that night.
If it was a $200 million dollar project, like Batman V Superman, yeah, 19 million would be disappointing.
Brokeback Mountain made $600,000 in it's first weekend, and 2.5 million in it's second. This movie isn't a bomb.