According to her campaign's poll, Heidi brings in 45 percent support to Berg's 42, within the poll's 4-point margin of error. Thirteen percent of those polled remain undecided.

Heitkamp seems to have much stronger crossover appeal, bringing in 11 percent Republicans, while Berg has the support of only 3 percent of Democrats. And the internal poll shows voters split about evenly in their views of Berg, with 42 percent viewing him favorably to 43 percent viewing him unfavorably, while 50 percent see Heitkamp favorably to only 38 percent who view her unfavorably.

It's a striking reversal of the last independent poll of the race, out on Saturday, which gave Berg 50 percent support to Heitkamp's 40, with 10 percent of voters still undecided. That poll, conducted by Essman/Research for the Fargo Forum, showed both splitting the electorate in terms of favorability.

The Forum poll, however, came under fire because of the low number of Democrats included in the survey. Only 19 percent of the poll's respondents were Democrats, an unusually low figure for a state that had Democrats at 28 percent of the electorate in 2008 exit polling.

The polling memo attached to Heitkamp's internal poll notes that low level of Democratic respondents, but doesn't give its own party breakdown. It was conducted by the Mellman Group among 600 likely voters from Oct. 16-19, and has a margin of error of plus or minus 4 percent.

Heitkamp's internal numbers come as her campaign releases a new ad, offering her position on cutting debt "for them," she says, over clips of children playing. In the ad, she pledges to fight for a balanced-budget amendment and cut wasteful spending, and offers her position that no senators should receive pay raises until the budget is balanced.

The new ad marks a slight shift in messaging in a race that has centered largely on more local issues, like the farm bill, and personal issues, like Berg's business connections and Heitkamp's campaign donations.