A new poll from a Democratic firm finds Colorado senator Mark Udall in a close race with the leading Republican challenger, House member Cory Gardner. PPP polls discovered in its poll of registered voters that 42 percent support Udall, the Democrat, while 40 percent would vote for Gardner. Another recent poll found a similar margin between the two candidates.

Gardner entered the race against Udall late last month, and his decision to run has seen other Republican candidates drop out, effectively clearing a path for the two-term congressman. Udall's poll numbers were seen as weak heading into his reelection effort this November, and the president's health care law, for which Udall voted, is unpopular in Colorado.

Meanwhile, the free-market organization Americans for Prosperity has launched its first ad in Colorado for the 2014 cycle. The ad targets Udall's support for Obamacare and is similar to ads being run in other states against vulnerable Democrats up for reelection.

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