Missouri Republican Ed Martin said Monday that he'll make a run for the House next year rather than wage a bid for the GOP nomination to challenge Sen. Claire McCaskill (D-Mo.).

With Rep. Todd Akin (R-Mo.) poised to enter the Senate race, Missouri's 2nd district is expected to be an open-seat race that could also attract Rep. Russ Carnahan (D-Mo.).

Martin made the switch official in a Monday morning radio interview and rolled out a new announcement video on his campaign website.

"There's a chance now to focus on running for the U.S. House," Martin said Monday. "I'm going to run for the Congress in the 2nd district."

Martin said he anticipates a primary. Republican Ann Wagner has formed an exploratory committee and appears to poised to run for the seat as well.

The latest polling on the Senate race had Akin in a dead heat with former state Treasurer Sarah Steelman (R). Akin took 29 percent of the vote to 28 for Steelman, but Martin was polling at just 9 percent.

Carnahan, meanwhile, is looking for new territory ahead of 2012 after the congressional map approved by the Republican-led State Legislature eliminated his district. A shift into the state's 2nd district could set up a rematch with Martin, who challenged him unsuccessfully in 2010.