I spoke with two staffers via a video conference call. At the time I was not living in DC, but I assume that anyone living in the DC metro area could have an in-person interview at the firm.
I honestly don't recall the specific questions that were asked during my interview, but I'm pretty sure they were basic questions that dealt with my career interests and my work experience. As long as you prepare well for the interview you'll be fine. Staffers are all very nice, and I really mean that; I've never had a work experience like this before where there were literally no "bad apples." Although everyone is busy most of the time, the staffers manage to be chill and friendly which I really appreciated during my internship.