The ads quote Heitkamp praising Obama, healthcare reform and other economic measures Obama has taken. Republicans also launched a website,, to document Heitkamp's support for Obama's policies.

“There’s a reason that her liberal friends in Washington are working to get Heidi HeitkampMary (Heidi) Kathryn HeitkampSenate rejects Trump immigration plan Cramer to announce North Dakota Senate run on Friday Senate Democrats not sold on bipartisan immigration deal MORE into the U.S. Senate race, because national Democrats know that she will stand behind them, instead of standing up for North Dakota,” said Matt Becker, a spokesman for the North Dakota GOP. “Whether it was her outspoken support for President Obama’s massive healthcare overhaul or his big government spending agenda, Heidi Heitkamp has been with President Obama every step of the way.”

While not in the race, Heitkamp is expected to announce within weeks that she will run for the Senate seat being vacated by retiring Sen. Kent Conrad (D-N.D.). So far, the only Democratic candidate in the race is Tom Potter, a professor without elective experience whom Democrats do not see as a formidable candidate against Berg.

Heitkamp did not respond to a request for comment, but the North Dakota Democratic-NPL party called it unfortunate that Republicans had gone already gone negative, pointing out that Republicans had failed to point out anything that Rep. Rick Berg (R-N.D.), the GOP front-runner to replace Conrad, had accomplished on behalf of the state.

"They want to start this off by misleading with political attacks here and quite frankly, North Dakotans don't appreciate that," said Andrew Zabel, the party's executive director. "We don't have to take full-age ads out to attack. We think the issues are on our side."

While North Dakota is seen as Republican territory, it sent only Democrats to Washington for almost two decades until 2010, when Republicans took control of one of the state's two Senate seats and its only House seat.

Democrats in Washington and in North Dakota have been eagerly courting Heitkamp, who has wide name recognition in the state, to run for the seat. Their other top choice, state Rep. Pam Gulleson (D), opted to run for Berg's House seat instead of trying for the Senate.

- This post was updated at 3:21 p.m. to add a response from Democrats.