DENVER — The second TV ad from the group Americans For Prosperity attacking Colorado Sen. Mark Udall focuses on the 335,000 health insurance policy cancellation letters mailed to Coloradans as a result of the Affordable Care Act that Udall supported.

That figure — 335,000 people whose “plans were cancelled due to Obamacare”, the ad’s narrator says — has been disputed by Democrats, who point out that 92 percent of those individuals were offered options to renew their coverage.

“Can you really afford to pay thousands more?” the female narrator asks. “Your health plan, cancelled. All because Mark Udall said ‘yes’ to Obamacare.”

The spot, which will run on Denver TV airwaves for the next three weeks, hits just as the billionaire Koch Brothers, whose fortune largely finances AFP, are becoming more of a focus in contested Senate races across the country.

Now that Democrats have been attacking the Koch Brothers as boogeyman billionaires for a few months, Republicans are starting to defend the duo.

Democrats viewed the shift as a sign that Republicans are moving away from efforts to focus Senate races solely on the issue of Obamacare, which saw more than 8 million Americans sign up for health insurance in the first six months of open enrollment under the new law, well surpassing the Obama administration’s long-held goal of enrolling 7 million Americans.

“The Republican effort to turn Senate races into referenda on the health care law has failed, and they are now scrambling to find an alternative strategy,” writes the Democratic Senatorial Campaign Committee’s Matt Canter in a memo out Wednesday.

Additionally, Democrats criticized the AFP ad’s use of an photograph of Udall standing next to President Obama, both with somber expressions, as the narrator remarks “…all because Mark Udall said yes to Obamacare.”

The image was taken in July 2012 at Children’s Hospital in Aurora moments after Obama and Udall met with family members of those killed and injured just days earlier in the Aurora theater shooting.

“Republican, Democrat or unaffiliated, all Coloradans can agree that using imagery from a visit to comfort the victims of the tragedy in Aurora is out-of-bounds for political attacks,” Chris Harris, Udall’s spokesman, told FOX31 Denver Wednesday.

Udall is facing a strong challenge from Republican Congressman Cory Gardner of Yuma, who abandoned a safe GOP seat and a sure shot at House leadership to go all-in on a Senate race that could determine control of the Senate next year.

Udall’s campaign has its own ad on the air attacking Gardner for supporting personhood measures and legislation to limit some birth control; and the League of Conservation Voters is also currently running TV ads attacking Gardner for his support of the oil and gas industry.