3 days ago, I flat out missed a flight for the first time in at least 6 years... because I didn't allow enough time for security at BWI. Like you, I knew I was cutting it close, but figured I'd be okay. And then the TSA Precheck line took 27 minutes, and I got to the gate at 4:05pm for a 4:12pm flight. Boom.
So, yeah, do NOT rely on getting through security in anything like a normal time. I'm not sure what the deal is at BWI, because the line wasn't egregiously long; it just moved amazingly slowly. I wonder if the existence of a CLEAR line had an effect -- have the CLEAR folks subtly influenced the Precheck line to move slower in order to incentivize buying CLEAR?
I usually fly WN from BWI. The precheck line is often 30 mins long. In fact, many times the standard line is shorter but I don't want to unpack everything, undress etc. I decided to sign up for Clear. $99 with a Delta number. Now, I can park in the daily garage and be at the gate in 10 mins.