Regional Jet 200 ER/LR (CRJ200)
Situational Awareness
Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Procedure; Airspace Structure; Human Factors
On the TRUPS ONE RNAV arrival into DCA; between RLLLL and LACKE at 6;000 feet we noticed traffic at our 12 o'clock; less than five miles ahead; roughly around 300 to 400 feet above us on the TCAS.  We confronted ATC and asked if they had traffic in front of us; the controller simply replied; 'Yes; there is traffic in front of you.' At this time we received a TCAS alert followed by an audible warning to monitor vertical speed.  We then complied with the RA and descended to avoid the traffic.  We notified ATC and were instructed to continue our descent to 4;000 feet.  In our descent we saw the traffic which appeared to be a light single engine aircraft.  We then continued on the arrival and landed in DCA uneventfully.  This event occurred due to the lack of assistance from ATC.  They could have simply given us a heading to avoid the traffic but instead gave us an ignorant response.
CRJ200 First Officer reports a TCAS RA during the TRUPS 1 arrival to DCA at 6;000 feet.  ATC does not seem concerned and issues a descent clearance only after a descent is initiated by the crew in compliance with the RA.