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 Finance: Senate punts on Zika funding | House panel clears final spending bill | Biz groups press Treasury on tax rules | Obama trade rep confident Pacific deal passes this year Overnight Healthcare: Lawmakers leave for summer without approving new Zika funds Dems block defense spending bill for second time 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 McCainPrimary opponent: McCain has 'issues about race' Clinton, Trump sharpen attacks The Hill's 12:30 Report MORE (Ariz.) and Lindsey GrahamLindsey GrahamClinton, Trump sharpen attacks Graham: Let special prosecutor probe Clinton emails The Trail 2016: Clinton’s ups and downs 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.