When people tell David Thomas they want to leave the Hill, he asks them to be sure they’ve thought the decision through. “The first thing I always ask is, ‘Are you truly ready? Are you going to miss being in the center of the action?’” he said. Thomas, 47, a partner at Mehlman, Castagnetti, Rosen & Thomas, left the Hill over a decade ago. He started out as an intern for Al Gore, when he served as a Tennessee senator, and he was California Democratic Rep. Zoe Lofgren’s chief of staff for four years.