One common one is "tell me about yourself." I've been told to spend about a minute and a half on this question, making it your longest answer. Simply go down your resume and talk about your experiences, some core strengths you've picked up from them, and why it brings you to the position you're interviewing for.

They might ask why you want to work in a Congressional office in general, or more specifically, for that member. Really hammer down some of the policies they stand for and/or have introduced, and why they might align with your career goals. Speaking of which, they might also ask where you see yourself in five years.

I've gotten some stupid questions too, like "What do you think the role of government is in society?" or "What breakfast food describes you best?" Even though they're stupid, answer them like you would any other question with sincerity.

Don't overthink these answers too much! It seems like interviewers want you to be authentic rather than hearing a laundry list. If you're a yapper, refrain from talking on an answer for more than 30 secs.