The DCA web site suggest 90-120 minutes is ample though the airport can at times get very busy, especially during holidays so a 3 hour window might be advisable, especially if your destination is international. Aim to leave home earlier during snowy weather and keep an eye on your flight status. If parking at or near the airport be aware of the walking or shuttle trip duration and factor that into your intinerary.
Your DCA security wait times at Washington Reagan Airport can be shortened with TSA PreCheck membership. Members benefit from a dedicated lane for identification and verification by TSA Check and quicker processing as theres no need to remove belts, shoes etc. Check out today's estimated TSA PreCheck wait times at DCA Airport above in addition to open lane info. To find out more about joining or renewing TSA PreCheck membership visit and the associated benefits visit https://www.tsa.gov/precheck.
Washington Regan Airport receives comparatively few International arrivals with most international travelers arriving at Washington Dulles or Baltimore Airport. Because of this you should expect to get processed promptly as you are unlikely to be in a long queue with other international visitors, as is often the experience at many large US airports.