Both the civil servants and the lobbyists.
My choice would be somewhere in say Kansas, Nebraska or in that vicinity...near the geographic center of the country and away from the inbred media, Wall Street, and the leaches like lobbyists and PACs. With the money we would save just from stopping ridicules spending brought on by these groups we could easily build a functioning city. DC could remain the center of our state department due to the number of embassies and closeness to NYC, the Supreme court could stay there and perhaps the Whitehouse but getting the Congress out of DC is imperitive.
2 Terms , 12 years in the Senate then the politician has to sit out 1 full term (6 years).
6 terms in House then the politician has 2 sit out 3 terms (6 years)
I would like to find some way of forcing them to leave Dc but that's not realistic. Most of these guys if they were forced out of the political limelight for even 1 term they would disappear politically. (If not actually!)