Just 34 percent of voters approve of the job Sen. Michael Bennet (D) has done since being appointed in January to replace Interior Secretary Ken Salazar, while 41 percent disapprove, according to a new automated poll released Wednesday.

But Bennet, who could face a competitive primary challenge, garnered a 59 percent approval rating from self-described Democrats. Just 16 percent of Democrats disapproved and 24 percent had no opinion.

The survey of 1,050 Colorado voters was conducted by the Democratic polling firm Public Policy Polling and was in the field April 17-19. It had a 3-point margin of error.

The poll also found that Bennet narrowly trailed former Rep. Bob Beauprez (R) in a hypothetical matchup, 43 percent to 42 percent. But the Senator led three other Republicans who have been mentioned as possible challengers.

He bested Aurora City Councilman Ryan Frazier 39 percent to 35 percent, Weld County District Attorney Ken Buck 40 percent to 34 percent and state Senate Minority Leader Josh Penry 41 percent to 34 percent.