Republican U.S. Senate candidate Kurt Bills campaign says a Star Tribune Minnesota Poll that shows incumbent Democrat Amy Klobuchar with a substantial lead in the race is biased, a charge that Star Tribune leaders dispute.

In a news release on Thursday, Bills campaign manager Mike Osskopp said the poll oversampled Democrats and said, "Don't forget, Amy's Dad was a columnist for the Star Tribune for 3 decades. It's no coincidence that they are pulling for Daddy's little girl." Later, Osskopp e-mailed a fundraising appeal to supporters that said "Daddy's newspaper needs to protect daddy's little girl."

Jim Klobuchar was a columnist with the newspaper for 30 years before retiring in 1996.

Said Star Tribune Editor Nancy Barnes: "The Star Tribune stands behind the results of this poll. We carefully selected Mason-Dixon for their deep experience and long track record of unbiased work in polling. Every poll has a margin of error, however. For that reason, we always consider polling to be a snapshot of what is going on in the electorate in any given period, rather than exact science."

The poll, conducted last week, found that 57 percent of likely voters favored Klobuchar, compared to 28 percent for Bills, a lead of 29 percentage points. More than 60 percent of those polled said they did not recognize Bills' name.

Bills' internal polling shows Klobuchar with a 15 percentage-point lead.

The Minnesota Poll of 800 likely voters, conducted Sept. 17-19, included 41 percent self-identified Democrats, 31 percent independents and 28 percent Republicans. Bills' internal poll found 35 percent Democrats, 40 percent independents and 25 percent Republicans.

A Minnesota Poll conducted in October 2006, when Klobuchar made her first Senate run, showed her with a 21 percentage-point lead over her GOP opponent. Klobuchar won that election by 20 percentage points.

Klobuchar's campaign declined to directly address Osskopp's comment. "The senator continues to work on behalf of the people of Minnesota, and that's all that matters to her," said Klobuchar's campaign manager, Justin Buoen.