Yes and no. He has run for governor before with little success. However, he is a powerful state senator due to the fact that his constituency is solid--the white Dems couldn't replace him--and the fact that the Dems hold a 1 seat majority in the Wisconsin senate. He has parlayed that into substantial authority in state budgetary affairs. The rumor locally is that the real force behind the exposure of the signature fraud is Chuck Chavla, the Democratic leader of the state senate. As far as the primary is concerned, George probably is the biggest threat to Tom Barrett. Barrett is a congressman from Milwaukee whose district disappeared in the last census/redistricting. Barrett stands to win most of the Milwaukee Dem vote against Kathleen Falk (Dane County [Madison] Executive) and Jim Doyle (Wis. Attorney General) because these two lefties have their power base in Madison. If George took the black vote (overwhelmingly in Milwaukee County) that cuts directly into Barrett's home base.
The mystery is why Upchuckwalla is backing a Milwaukee RAT in Barrett instead of a fellow Madistan RAT.