Sen. Richard Lugar (R-Ind.) is trailing his primary opponent by at least 10% and may become the most senior credit union-backed legislator to lose a primary challenge this year.
Richard Gose, senior vice president for political affairs for CUNA, reported that the Credit Union Legislative Action Council, CUNA's political action committee, has donated the maximum amount it can to Lugar's campaign.
Lugar has held the seat since 1976 and is the most senior Republican senator.
Lugar is running against Richard Mourdock, a two-term state treasurer backed by the state's Tea Party.
Issues in the race include whether Lugar lives in Indiana and whether he is conservative enough.