An hour and 45 minutes before the flight to depart downtown DC? A lot of people would argue that's too much time.

Metro will take at worst, 25 minutes. It's rush-hour, so you are unlikely to wait for a train more than 5-6 minutes.

TSA precheck is highly unlikely to take more than 10 minutes.

Assume 10 minutes to walk from metro to security and 3 minutes from security to the gate - you are likely to be at your gate in 45 - 50 minutes.