Seniority is not granted based on years in Congress. It is based on years in Congress AND party. Thats how it goes. He switched parties (only so he could get re-elected next time) then proceeded to support a Republican over a Democrat, among other things. He thought he could keep his cake and eat it too but surprise, surprise. The World doesn't work that way. And Reid is not the only one to vote on this issue. He has ONE vote.