Indiana Treasurer Richard Mourdock speaks to supporters in Indianapolis, Tuesday, May 8, 2012, after he defeated incumbent Sen. Richard Lugar, R-Ind., in the primary. (AP Photo/AJ Mast)
Campaign cash from outside political groups is flooding into conservative states with close Senate races like Indiana and Montana, where residents are less accustomed to a relentless barrage of attack ads on TV.
Outside groups are spending another $1.5 million in Indiana's deadlocked Senate race this week.
A collaboration of Democratic-aligned groups announced plans Tuesday to spend $1 million on an ad attacking Republican Richard Mourdock for opposing the Chrysler bankruptcy in 2009.
The anti-tax Club for Growth, meanwhile, said it would spend $500,000 in Indiana.
This week has become the most expensive of any Indiana Senate battle as groups bought a $2.75 million of air time.
Mourdock spent $300,000 Monday on a new ad attacking Democrat Joe Donnelly for being "too liberal," and Senate Democrats spent another $439,000.
A Republican tracking ad buys confirmed Tuesday that the National Republican Senatorial Committee was spending $500,000 this week. The Republican requested anonymity because the NRSC does not openly talk about numbers.
While the most expensive Senate battles are being fought in presidential battlegrounds like Florida, Ohio and Virginia, Republican-leaning states like North Dakota and Arizona aren't being left out.
Campaign finance expert Darrell West says outside groups get more bang for their buck in smaller markets like Fargo, N.D. For example, Karl Rove's Crossroads groups announced $4 million in ad buys Tuesday targeting competitive Senate races in North Dakota and Montana as well as Florida and Virginia.
Despite a 2-to-1 outside spending advantage, GOP chances of taking control of the Senate have shrunk recently.