Washington (CNN) - Americans for Prosperity is adding Sen. Mark Udall of Colorado to their list of Democratic senators facing tough re-elections this year that the conservative group is targeting.
The group, backed by the deep pockets of the billionaire industrialist brothers, David and Charles Koch, says it's going to spend just under $1 million starting Monday to run a TV commercial that criticizes Udall for his support of the health care law.
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"Millions have lost their health insurance, millions can't see their own doctors, and millions are paying more and getting less," says a women who narrates the AFP spot. "Obamacare doesn't work. It just doesn't work. Tell Senator Udall to stop thinking about politics and start thinking about people."
Republicans have been fiercely attacking President Barack Obama and Democrats over insurance polices dropped due to new standards in the Affordable Care Act. Neither the government nor the insurance industry catalogs how many people have lost their policies.
The AFP ad comes just a few weeks after GOP Rep. Cory Gardener announced he would challenge Udall, potentially making the first term senator's re-election much more challenging. Two other Republicans running for the Senate nomination dropped their bids after Gardener jumped in.
The group says it's spending $700,000 to run the same spot against another Democratic senator facing a difficult re-election, Mary Landrieu of Lousiana.
AFP has been the biggest spender to date this election cycle, shelling out around $30 million since October to run ads, most of them focused on health care, that attack Democrats and praise Republicans.
"Cory Gardner's special interest out of state allies are dumping their millions into Colorado because they know he will push an agenda in Washington that's good for billionaires like the Kochs but bad for Colorado's middle class," Democratic Senatorial Campaign Committee Press Secretary Justin Barasky told CNN. "Gardner is counting on millions in out of state money to attack Mark Udall because he desperately wants to hide just how out of step he is with mainstream Coloradans."
Democrats hold a 55-45 majority in the Senate (53 Democrats and two independents who caucus with the party), but are defending 21 of the 36 seats up in November, with half of those Democratic-held seats in red or purple states, like Louisiana and Colorado
Senate Majority Leader Harry Reid has repeatedly attacked the Koch brothers as being "un-American" and having "no conscience," and he's argued that the "vast majority" of the AFP ads are untrue.