As of this morning, Four Mile Run trail has a few patches of minor snow ice between Blumont and Columbia Pike but is then clear to the Potomac. I have studded tires so was fine; probably would have been fine on cyclocross tires. Only one area at the Route 50 underpass would a road bike need to have been real careful or walked.
Mt. Vernon trail is clear except two areas of “wash over” ice between 14th Street Bridge and Memorial Bridge. These were sheet ice, but you could ride around them in the grass — I rode over them with my studded tires
Custis from Key Bridge to Glebe Road is clear. Only a few small patches of ice that can easily be avoided.