Ed Martin jumped into the Missouri Senate race today, giving former state Treasurer Sarah Steelman a top primary opponent less than a week after former Sen. Jim Talent decided he would not enter the Republican primary.

Democratic Sen. Claire McCaskill is up for re-election in 2012, and she's a top target of the National Republican Senatorial Committee, not least because she'll be running in a tough state for Democrats when President Obama is also on the ballot for re-election.

Talent indicated late last year to RealClearPolitics that he was taking a careful look at the race and was inclined to run, but he announced last week that he had changed his mind.

Before Talent decided not to run, however, Steelman, who also considered running in Missouri's open Senate race in 2010, was the first candidate to jump into the field. She was joined Monday by Martin, a chief of staff to former Republican Gov. Matt Blunt.

Martin ran for Congress unsuccessfully in 2010 against Democratic Rep. Russ Carnahan in his St. Louis-area district. But his aggressive campaign in the Democratic-leaning metropolitan area made the race competitive and got the attention of national Republicans.

In his announcement video on Monday, Martin said, "I believe that the election in 2012 will come down to a very simple question: What should the size, scope and cost of the federal government be?"

He goes on to voice his support for a balanced budget amendment and attempts to tie McCaskill to Obama, attacking them both on government spending, bailouts and health care.

McCaskill, however, has taken a hardline stance against the administration at times for overspending.

The video, which features Martin speaking directly into the camera for three minutes against a white back-drop, appears to mimic the style of a long TV ad Republican Sen. Marco Rubio of Florida cut last year in his successful campaign.

Steelman said in a statement on Martin's entry, "I am running to fight for Missouri families who want less government and more freedom. I remain focused on running against Senators Claire McCaskill and Harry Reid's control of the U.S. Senate."

GOP operatives in Missouri have said Steelman is unlikely to lock up support throughout the state, and that if Martin can rally Republican donors in St. Louis while keeping former Ambassador Ann Wagner out of the race, he'll have a serious shot at the Republican nomination.

The Democratic Senatorial Campaign Committee already is previewing its line of attack on Martin: "Nothing says outsider like a failed Congressional candidate and chief of staff to a failed former Governor turned-lobbyist."

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