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 DonnellyTrump’s vow on Medicare in doubt after HHS choice Red-state Dems face tough votes on Trump picks Red-state Democrat: I'll oppose Trump's health chief 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 McCainThe trouble with Rex Tillerson Senate: Act now to save Ukraine A Cabinet position for Petraeus; disciplinary actions for Broadwell after affair MORE (Ariz.) and Lindsey GrahamLindsey GrahamThe trouble with Rex Tillerson A Cabinet position for Petraeus; disciplinary actions for Broadwell after affair Pentagon should have a civilian chief to give peace a chance 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.