The Hoosier State officially became a Senate battleground last week as both parties dropped six-figure ad buys into the race.

During the weekend, the National Republican Senatorial Committee bought $650,000 worth of airtime for a week-long buy to boost its nominee, state Treasurer Richard Mourdock, Roll Call confirmed.

The buy comes just days after the Democratic Senatorial Campaign Committee purchased $516,000 worth of airtime to help Rep. Joe Donnelly, the Democratic nominee.

During the summer, the Indiana Senate seat catapulted into the top tier of contested races. Roll Call continues to rate the race as Leans Republican but will re-evaluate that determination in the coming days.

For months, Democrats insisted the race was competitive, releasing several internal campaign polls showing Donnelly tied with Mourdock.

Also this morning, Donnelly’s campaign released another internal poll showing him 3 points ahead of Mourdock. In the Global Strategy Group survey taken Sept. 10-12, Donnelly leads Mourdock, 45 percent to 42 percent, among 800 likely voters (see the full polling memo here).