Sen. Heidi Heitkamp (D-N.D.) has a new ad attacking her Republican opponent, U.S. Rep. Kevin Cramer, for paying his wife more than $150,000 out of his campaign account.

The ad is the moderate Democrat’s most direct shot at Cramer so far in the campaign and the first ad to mention Cramer’s history of paying family members out of his campaign funds. The pair are locked in a tight race, and Heitkamp is considered perhaps the most vulnerable Democratic senator in the country. President Donald Trump won North Dakota by more than 30 percentage points in 2016, and Republicans hope a victory in North Dakota would extinguish Democratic hopes of winning the Senate.

The 30-second spot also attacks Cramer for hiking utility rates after taking donations from oil and gas companies, and for raising his own pay when he was a member of the Public Service Commission.

“Who comes first?” a male narrator asks in the ad, which was provided first to HuffPost. “Special interests and himself. Who comes last? Us.”

Cramer paid his wife to serve as his campaign manager during cycles when he wasn’t facing a serious challenge. He also paid other family members, including once giving his daughter $300 to babysit during an event.

Paying family members with campaign money is legal as long as they aren’t paid above market rate, but ethics experts have questioned the practice. Sen. Dean Heller (R-Nev.) and Sen. Joe Manchin (D-W.Va.) have both paid family members with campaign cash this cycle.

North Dakota Republicans dismissed the ad as an attempt to distract voters from Heitkamp’s record.

“Heidi Heitkamp’s campaign is built on lies, misinformation, and manufactured controversy; and this ad is nothing new,” North Dakota GOP spokesman Jake Wilkins said. “Heitkamp should focus on serving her constituents and answering for her out-of-touch liberal record instead of baselessly attacking her opponents while running from tough questions.”