"[I]t would certainly make a difference if Lugar campaigned actively for Mourdock"

The bruised feelings of retiring Senate centrists have created headaches for Republican and Democratic leaders who are trying to keep control of their seats.

Sens. Dick Lugar (R-Ind.), Olympia Snowe (R-Maine) and Joe Lieberman (I-Conn.) are staying aloof from the battles for the seats they are vacating, giving challengers a better chance of flipping them…

Mourdock’s weak support among centrist Republicans has emerged as one of the biggest stumbling blocks to his campaign.

“It’s obvious that the Lugar voters are the key here,” said Peri Arnold, professor of political science at Notre Dame University.

“If [Lugar] had fully embraced and done some campaigning for Mourdock, it would have put a stamp of acceptability on Mourdock. The fact that he has been so lukewarm has peeled off some support.”