Where are you located? The easiest and most straight forward way would be MARC communter trains or Amtrak from DC to Harpers Ferry, WV. Then simply cross the bridge over the Potomac River.

I took the Amtrak into DC and back.
The Harpers Ferry station is about 50 yards off the trail.

when looking at the schedules it looked like the MARC train to HF involved a bus connection at the end. Does anyone know of this is correct? Amtrak train goes right to the station. Commuter trains don't run on weekends either.

Last time I took MARC was from Harpers Ferry to DC. No bus involved.

DC to Harpers Ferry should not involve a bus as that line goes all the way to Martinsburg, WV.

Further edit.

Looking at the timetable it appears there are a few times a bus is involved. Also, be aware not all departures from DC actually go all the way to Harpers Ferry.

Last summer I made the trip three times. DC-HF twice on Amtrak and HF-DC once. The extra $3 for Amtrak (14 v. 11) was well worth it for me.