Incumbent Democratic Sen. Heidi Heitkamp is out with her third ad of the election cycle, and it's following a familiar theme: Touting her bipartisanship and her willingness to work with President Donald Trump. 

"When I ran for the Senate six years ago, I said I wouldn't vote the party line, because I don't think either party has all the answers," she says in the new ad. "That's why I voted over half the time with President Trump. And that made a lot of people in Washington mad, but when I agree with him, I vote with him." 

The newest Heitkamp ad comes as her Republican opponent, Kevin Cramer, is making plain his frustration with Trump's complimentary words for Heitkamp. 

In an interview published Monday by the Washington Post, Cramer suggested that Trump has declined to criticize Heitkamp as harshly as other Democrats because of her gender. 

“I do think there’s a little difference in that she’s a woman,” Cramer said. “That’s probably part of it — that she’s a, you know, a female. He doesn’t want to be that aggressive, maybe. I don’t know.”