MADISON, Wis. — The election for U.S. Senate in Wisconsin is a year off, but the television advertising battle is well underway.

The Democratic Senate Majority PAC announced Tuesday it is launching a $1 million television and digital ad campaign to support incumbent Sen. Tammy Baldwin. The spot comes a week after a conservative group funded by the billionaire Koch brothers launched a $1.6 million ad campaign targeting Baldwin.

Both ads focus on Baldwin’s position on taxes as Republicans are pushing a tax system overhaul. The new pro-Baldwin spot refers to the ad by the Freedom Partners Chamber of Commerce and says Baldwin is being “smeared” because she’s fighting a tax system that protects the wealthy.

The ad says Baldwin has voted more than 50 times to cut taxes for the middle class.