INDIANAPOLIS (AP) — Democrats Indiana is becoming a major battleground in the race for control of the Senate, with national Republicans and Democrats sending more cash this week to tea party favorite Richard Mourdock and Democrat Joe Donnelly.

Republicans, who must gain four seats nationally to take control of the Senate, have spent $300,000 to Mourdock for attack ads this week. The Democratic Senatorial Campaign Committee, meanwhile, is spending $439,000 in the state in coming days on Donnelly's behalf.

A Democratic source tracking ad spending confirmed the new buys on background because campaigns will not openly talk about how much they are spending.

The Mourdock campaign has spent another $300,000 on Indiana's airwaves this week, bringing the total spent so far to more than $8 million.