Mourdock beat incumbent Sen. Dick Lugar (R-Ind.) in the Republican primary earlier this year and is facing a tougher than expected challenge from Democratic Rep. Joe DonnellyJoe DonnellyOvernight Energy: Judges scrutinize Obama climate rule Funding bill rejected as shutdown nears Dem presses Congress to pass veteran suicide measure MORE (Ind.). Lugar decided not to help or campaign for Mourdock after he was defeated in the primary.
Other Republican senators, such as John McCainJohn McCainGreen Beret awarded for heroism during 'pandemonium' of Boston bombing House passes bill exempting some from ObamaCare mandate NBC's Lester Holt emerges from debate bruised and partisan MORE (Ariz.) and Lindsey GrahamLindsey GrahamObama nominates ambassador to Cuba Funding bill rejected as shutdown nears Shutdown risk grows over Flint MORE (S.C.), have gone to Indiana to campaign for Mourdock.
The Indiana seat is viewed as a critical win in order for Republicans to get control of the Senate.
Democrats are defending 23 Senate seats compared to just 10 Republican seats, but thanks to good recruiting and a few GOP fumbles, Democrats have been able to stay competitive in states — such as Indiana, Missouri, North Dakota and Maine — that were once thought of as potentially easy pick-ups for Republicans.