“John Boehner is having a difficult time in his caucus.”
“How do I deal with all these groups in my caucus?”
“He tried to be a reasonable man with his caucus.”
1763, Amer.Eng., perhaps from caucauasu "counselor, elder, adviser" in the Algonquian dialect of Virginia, or the Caucus Club of Boston, a 1760s social & political club whose name possibly derived from Mod.Gk. kaukos "drinking cup." Another candidate is caulker's (meeting). The verb is from 1850.
IT'S THE CAUCUS STUPID!