Democrats are turning their fire on Scott Rasmussen, the prolific independent pollster whose surveys on elections, President Obama’s popularity and a host of other issues are surfacing in the media with increasing frequency.

The pointed attacks reflect a hardening conventional wisdom among prominent liberal bloggers and many Democrats that Rasmussen Reports polls are, at best, the result of a flawed polling model and, at worst, designed to undermine Democratic politicians and the party’s national agenda.

On progressive-oriented websites, anti-Rasmussen sentiment is an article of faith. “Rasmussen Caught With Their Thumb on the Scale,” blared the Daily Kos this summer. “Rasmussen Reports, You Decide,” the blog Swing State Project recently headlined in a play on the Fox News motto.

“I don’t think there are Republican polling firms that get as good a result as Rasmussen does,” said Eric Boehlert, a senior fellow with Media Matters, a progressive research center. “His data looks like it all comes out of the RNC [Republican National Committee].”

“Whether intended or not, Rasmussen polls have been used by conservative voices as talking points, and when that happens on one side it inevitably produces a reaction from the other,” explained Mark Blumenthal, a polling analyst and the editor and publisher of Pollster.com. “Rasmussen produces a lot of data that appear to produce narratives conservatives are promoting, and that causes a reaction.”

While Scott Rasmussen, the firm’s president, contends that he has no ax to grind — his bio notes that he has been “an independent pollster for more than a decade” and “has never been a campaign pollster or consultant for candidates seeking office” — his opponents on the left insist he is the hand that feeds conservative talkers a daily trove of negative numbers that provides grist for attacks on Obama and the Democratic Party.

Nothing, however, sets off liberal teeth gnashing more than Rasmussen’s daily presidential tracking polls, which throughout the year have consistently placed Obama’s approval numbers around 5 percentage points lower than other polling outfits.

“He polls less favorably for Democrats, and that’s why he’s become a lightning rod,” said Charles Franklin, a University of Wisconsin political scientist who studies polling. “It’s clear that his results are typically more Republican than the other person’s results.”

On Saturday, Dec. 26, for example, Rasmussen’s daily tracking had Obama’s approval at 44 percent, with a disapproval figure of 56 percent. A Real Clear Politics compilation of other pollsters, meanwhile, showed Obama with an average approval figure of 49.5 percent and disapproval of 45.1 percent.

“He’s been underpolling Obama all year,” said Boehlert. “People start thinking, ‘There’s something going on here.’”