The Democratic Senate Majority PAC is tying Iowa Senate candidate Joni Ernst (R) to Charles and David Koch in a new ad, the group's latest attempt to get voters to distrust her campaign.

"Out-of-state oil billionaires, the Koch brothers, are spending millions supporting Joni Ernst's campaign. Why? Because Joni Ernst shares their priorities: A scheme privatizing Social Security and a plan cutting Medicare's guaranteed benefit all to pay for more tax breaks for oil billionaires," the ad's narrator says. "If Joni Ernst's got their back, we can't trust her to protect ours."

The ad is the latest in a flurry of Democratic attacks following acknowledgement of a tight race in Iowa. Rep. Bruce BraleyBruce Lowell BraleyOPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer MORE (D-Iowa), her Democratic opponent, has made some missteps in the race, and if Republicans can pick off this open seat, their path to the Senate majority would be considerably easier.

The race is just getting underway following Ernst's midsummer primary win, unlike many other Senate battles where both sides have been on the air for months. Recent polling shows a coin-flip race.