DCA has been horiffic lately during rush hour, i.e. early morning and 5-7pm. I'm talking 30 plus minutes with few TSA lines open on the main terminal. MWAA admits they are having problems and working on it.
That said B6 is in the A concourse and even if TSA is fully staffed, there are only three (I believe) X-Rays, so it can move slow if there are a lot of flights.