Somebody is trying to upset Montana’s Senate race. The problem is, nobody can figure out exactly who it is.

Montana is seen as a key to Republicans winning back control of the Senate — barring upsets. Four-term Republican Rep. Denny Rehberg is challenging Jon Tester, incumbent Democratic junior senator, who barely won in 2006. Rehberg already represents the entire state as its at-large member of Congress, so name recognition is no problem.