Senate Democrats' campaign arm is hitting the airwaves in the Iowa Senate race beginning Tuesday with a sizeable advertising buy that comes as polls show a close contest between state Sen. Joni Ernst (R) and Rep. Bruce Braley (D).

The Democratic Senatorial Campaign Committee commercial charges that's Ernst's ideas "are just too extreme for Iowa." It says she wants to privatize Social Security.

The committee has reserved more than $500,000 in broadcast air time over the next two weeks in four media markets, according to public records. The buy comes as a pair of recent polls from NBC News/Marist and Quinnipiac University have shown a close race.

"Joni will protect social security for seniors like her parents, and ensure it's there for generations to come, like her daughters and grandchildren," responded Ernst spokeswoman Gretchen Hamel in a statement.

NBC News/Marist, the most recent poll taken, showed Braley and Ernst deadlocked at 43 percent.

Iowa is increasingly shaping up as a key battleground in the fight for the Senate majority. Republicans need to pick up six seats to win control of the chamber.

Ernst is on active duty with the Iowa Army National Guard though Friday. Allies and opponents have engaged in an ad war in her absence.

A pair of Republican groups are on the air giving Ernst cover: The Koch-backed Americans for Prosperity and American Crossroads, which was co-founded by Karl Rove.