The results are different than previous polling in the race, which has indicated a closer contest – including several Democratic polls that showed Heitkamp with the advantage.
Rasmussen conducted a telephone survey of 500 likely North Dakota voters on July 10-11.
The survey found 49 percent support Berg, while 40 percent support Heitkamp. Two percent preferred some other candidate, and 8 percent were undecided.
The results have a margin of error of plus or minus 4.5 percentage points.
Republicans were quick to praise the new poll’s findings.
“It’s clear that North Dakota voters are becoming increasingly turned off by (Heitkamp’s) campaign of negative and misleading attacks,” Berg spokesman Chris Van Guilder said in a statement, touting Berg’s “strong grassroots support throughout the state.”
Berg’s campaign also used the news in an e-mailed fundraising pitch to donors Thursday night.
Meanwhile, Democrats sought to discredit the findings in light of the pollster’s reputation.
Rasmussen Reports has a track record of a conservative-leaning methodology, which Democrats say calls into question the reliability of the results. Founder Scott Rasmussen also has ties to the Republican Party.
“This race is competitive because Heidi Heitkamp is willing to put the partisan gridlock aside to create jobs, to cut spending, get the budget under control and stand up for North Dakota,” Heitkamp campaign spokesman Brandon Lorenz said in a statement. “Rasmussen is a deeply flawed company discredited even by Republicans for botching results in multiple races.”
However, two years ago, Rasmussen’s surveys of North Dakota’s U.S. House race accurately predicted the outcome.
For eight straight months, Rasmussen polling found Berg ahead of longtime Democratic incumbent Earl Pomeroy. On Election Day 2010, Berg beat Pomeroy by nine percentage points.
This year’s Berg-Heitkamp battle continues to be in the national spotlight, because the outcome of the race could help tip the balance of power in the Senate next year.
Last month, a poll from Valley News Live and Bismarck-based KFYR found Heitkamp leading Berg, 47 percent to 46 percent with 7 percent of likely voters undecided.
Three Democratic-sponsored polls since November have also found Heitkamp ahead of Berg by between 1 and 5 percentage points.
In contrast, a Forum Communications Co. poll of likely primary voters in May found 51 percent favored Berg, while 44 percent liked Heitkamp and 5 percent were still undecided.
Most independent analysts gauging North Dakota’s race qualify it as either a “toss-up” or one that “leans Republican.”