Senate Majority PAC launching ads in Colo.

A major Democratic super-PAC is going on air in Colorado just days after a Republican group launched ads hitting Sen. Mark Udall (D-Colo.).

{mosads}Senate Majority PAC (SMP) is spending $500,000 to air ads across the state, launching this Sunday, that question the credibility of attack ads launched this week on a $970,000 buy by Americans for Prosperity (AFP), which is backed by conservative billionaires Charles and David Koch.

It’s part of a $3 million offensive effort by Senate Majority PAC to respond to Americans for Prosperity attacks in five states with competitive Senate races: Arkansas, Colorado, Louisiana, Michigan and North Carolina. The Democratic group is spending about $500,000 on two weeks of ads in every state but North Carolina, where it’s investing $1 million, as first reported by The New York Times.

The Colorado Senate race became more competitive for Republicans with the entry of Rep. Cory Gardner in the Republican primary. He’s largely cleared the field, and though Republican state Sen. Randy Baumgardner said this week he’s still in, Gardner is expected to easily pick up the nomination.

The Senate Majority PAC ad takes direct aim at the AFP ad, which features a woman speaking direct-to-camera about why “ObamaCare just doesn’t work.” The woman, the SMP ad points out, is an actress, and she’s been widely used in other AFP ads. The SMP ad also declares that those airing the ads are “insurance companies and out of state billionaires supporting Cory Gardner.”

And it charges that Gardner would end the Medicare guarantee, costing seniors.

“The more we learn about Cory Gardner, the more troubling it is,” the narrator adds.

The Koch brothers have spent at least $30 million since August on anti-ObamaCare ads in states with competitive Senate races, and their investment in Colorado — their first there this cycle — is a signal Republicans are bullish on their chances there.

Senate Majority PAC has countered AFP in many races, but with much smaller buys, though the $3 million investment indicates they might be ramping up their efforts. Still, Democrats openly admit they expect to be outspent on air this cycle.

They believe, however, direct attacks on the Koch brothers and the substance of the ads they’re running could help them counter some of the AFP’s attacks, and they are hoping a significant investment in their turnout operation in competitive states will help them hold their six-seat majority in the Senate.