The D.C. Metro system is undergoing a crisis of management and safety failures, and might very well undergo a larger crisis of shutdowns to fix things.
fwiw
See the local news re D.C. Metro subways.
Agree with mbarker12474. Metro might shut down for a while.
That being said, Trinity is apparently near the red line so there will be a transfer involved to get to Capitol Hill. Trinity University runs a shuttle to metro but you might want to call to see if it (a) runs during summer and (b) if non-students can use it. I’m guessing “yes” on both counts but you might want to be sure.
Too bad about Metro having problems - I visited DC once a year for a training event from 2003-05 and found the system to be a great way to get around quickly, including coming from BWI on MARC to transfer to Metro Red Line and go out to Gaithersburg MD.
For the OP, hope it works out well for your son as it sounds like a great experience. Perhaps the solution to dealing with Metro is the bus system. I’m not familiar with the surroundings of Trinity.
Trinity College is part of what is called Little Rome. It is a nice enclave in that part of DC. The whole area is owned by the Catholic Church and includes several seminaries, monasteries, Catholic University and the Basilica of the National Shrine of the Immaculate Conception. Lots of green spaces. I felt safe when I have visited there during the daytime although not sure at night. The outside areas are ify.