Democratic hopes for retaining the open Senate seat in North Dakota were given a major lift Tuesday as Heidi HeitkampMary (Heidi) Kathryn HeitkampVirginia loss lays bare Democrats' struggle with rural voters Washington's oldest contact sport: Lobbyists scrum to dilute or kill Democrats' tax bill Progressives prepare to launch counterattack in tax fight MORE, a former state attorney general, announced her bid to replace retiring Sen. Kent Conrad (D-N.D.).

With Heitkamp’s widely anticipated run now a certainty, Democrats instantly christened the race “the new toss-up,” while Republicans warned North Dakota voters that a vote for Heitkamp would be another vote for President Obama’s agenda.

“I’m running for the United States Senate because Washington is badly broken and our state needs an independent voice who will go there to stand up for North Dakota. With me, the people of North Dakota always have and always will come first,” Heitkamp said in announcing her candidacy.

Heitkamp’s entrance into the race was desperately sought by Democrats nationally and statewide, who were vigorously recruiting her to run against Rep. Rick Berg (N.D.), the Republican front-runner to replace Conrad. But as the one-year-until-election mark approached and Heitkamp’s candidacy remained a question mark, it raised the specter that Democrats would essentially cede the Senate seat to Berg. 

Democrats had also worked to recruit former state Rep. Pam Gulleson (D) to run for Senate, but she opted instead to run for the House seat Berg is vacating. Republicans called that decision a signal that Democrats considered a race against Berg to be a losing proposition.

"This is great news," Conrad said in a statement, adding that Heitkamp has North Dakota "in her DNA" and that he worked closely with her for more than 20 years. "She is exceptionally talented. Heidi has the experience, knowledge and background to deal with the critical issues facing North Dakota's families, farmers, and business owners."

Heitkamp joins Thomas Potter, a former professor from Grand Forks, N.D., in the Democratic primary. But Potter is not expected to pose a major threat to Heitkamp, who served as the state’s top law enforcement official from 1993-2000, ran unsuccessfully for governor and has wide recognition throughout the state.

As attorney general, Heitkamp made a name for herself taking on the tobacco industry, securing a landmark settlement with the largest tobacco companies and spearheading efforts to use that settlement to discourage smoking. Her brother, Joel Heitkamp, is a prominent radio show host in North Dakota.

On Tuesday, Heitkamp announced she was opening a campaign committee, clearing the way for her to start raising funds and building a campaign infrastructure, but said a formal announcement and campaign kickoff would be forthcoming.

Heitkamp’s announcement comes as Democrats work to stop the bleeding from North Dakota’s congressional delegation. Although a Republican-leaning state that reliably chooses GOP presidential candidates, North Dakota sent only Democrats to Congress for almost 18 years — until 2010.

Amid the Republican wave that brought 63 GOP freshmen to the House, gave control of the lower chamber over to Republicans and narrowed the Democratic majority in the Senate, retiring Sen. Byron Dorgan (D-N.D.) was replaced in 2010 by now-Sen. John HoevenJohn Henry HoevenEquilibrium/Sustainability — Presented by Southern Company — Native solar startups see business as activism Religious institutions say infrastructure funds will help model sustainability House passes legislation to strengthen federal cybersecurity workforce MORE (N.D.), who was at the time the state’s wildly popular Republican governor. To make matters worse for Democrats, former Rep. Earl Pomeroy (D-N.D.), who held North Dakota’s lone House seat for nine terms, was defeated by Berg by almost 10 points.

With the impending retirement of Conrad, one of the most influential members of the Senate, Democrats are eager to demonstrate that North Dakota is still competitive territory — especially as they work to retain control of the Senate. Republicans need to flip four Senate seats to take control away from Democrats, and a loss in North Dakota would make the Democrats’ challenge to hold their majority even more difficult.

“As of today, with Heidi Heitkamp’s announcement, the race to replace Conrad is officially a toss-up,” said Guy Cecil, the executive director of the Democratic Senatorial Campaign Committee.

Cecil pointed to a poll conducted in August by Democratic pollster Geoff Garin showing that Berg has only a four-point lead against a generic Democrat. Since Heitkamp is not a generic Democrat but a respected and established figure in the state, her candidacy poses an even more substantial threat to Berg, Cecil said.

But Republicans framed her as a shill for Obama, listing off her previous statements in support of healthcare reform and the Troubled Asset Relief Program.

“Now she wants to go to Washington to help President Obama enact his liberal agenda, which the vast majority of North Dakotans don’t support,” said North Dakota Republican Party Chairman Stan Stein. “It’s clear that President Obama wants Heidi Heitkamp in Washington, but North Dakotans need a United States senator who’ll stand up for our values and best interests.”

National Republican Senatorial Committee spokesman Brian Walsh argued that while 2010 was a major loss for Democrats in North Dakota, the writing on the wall indicates 2012 will be even tougher, with voters increasingly impatient over the lack of progress on the economy under Obama. "If North Dakotans want four more years of President Obama's tax-and-spend agenda then Heidi is their candidate," Walsh said. 

One additional hurdle for Heitkamp to cross as a late entrant into the race will be in the fundraising realm. Berg, a Tea Party-backed Republican, has been campaigning heavily for months, and had just over $1 million cash on hand to fund his campaign as of the end of September.

- This post was updated at 4:10 p.m.