Rep. Todd Akin (R-Mo.) will run for Senate in 2012. (Haraz N. Ghanbari/AP Photo)

"I am today announcing my candidacy for the United States Senate because of my deep concern about the condition of our economy, the debt, and excessive federal spending,” Akin told supporters in the St. Louis suburb of Creve Coeur. “I am deeply grateful for the support and encouragement I have received from fellow Missourians who share my convictions.”

Akin was elected to the House in 2000, representing the suburban St. Louis 2nd district. The seat was previously held by then-Rep. Jim Talent, who left Congress for an unsuccessful gubernatorial run. Before he entered Congress, Akin served six terms in the Missouri state House of Representatives. He is known as one of the most conservative members of the House.

While some Republicans are hoping that the six-term congressman will clear the GOP field, others are holding out to see who else gets in the race. Former state party chairwoman Ann Wagner and former congressional candidate Ed Martin both opted to vie for Akin’s House seat rather than compete with him in the primary. But St. Louis businessman John Brunner is likely to run and could be a strong contender, and former state Treasurer Sarah Steelman is in the race already.

There’s been some concern among Republicans about the weakness of their field in this race. Akin is a relatively low-profile congressman who sits in a reliably Republican district and hasn’t faced a competitive race since his first primary, over a decade ago. On the other hand, he has already raised more than Steelman, who had a lackluster first quarter. Brunner is indepently wealthy and willing to contribute some of his personal fortune to a campaign.

Steelman responded quickly to Akin’s launch with a statement of her own, decrying the "status quo in Washington” and saying she looks forward to a “vigorous debate.”

The Democratic interest group EMILY’s List was also quick to respond to Akin’s announcement. “He’s already one of the worst offenders in the Republican war on women, and now he wants to take his appalling agenda statewide,” said the group’s president, Stephanie Schriock, in a statement. “I have one question for him: You sold out the women of Missouri, and you want a promotion for that?”

Caitlin Legacki, spokeswoman for the Missouri Democratic Party, also responded: “In what will surely be a long, messy and expensive GOP primary, Missouri voters expect Todd Akin to answer a lot of important questions about where he really stands."

Republicans will put up a serious fight here no matter who their candidate is. McCaskill is a vulnerable freshman in a swing state, who has been further wounded by a scandal over a failure to pay taxes on a private plane that hits directly at the transparency-based personal brand she has created. She beat Talent by only three points in her 2006 election; the state went for Sen. John McCain (R-Ariz.) in the 2008 presidential race.

“While we don’t yet know who the GOP nominee will ultimately be, it’s safe to say that Republican will not have failed to pay almost $400,000 in back taxes on their private plane.” said National Republican Senatorial Committee spokesman Chris Bond.

The race to replace Akin in the House is already heating up. Along with Martin and Wagner, state Sen. Jane Cunningham is ”very highly interested.”