Former state Treasurer Sarah Steelman became the first Republican to announce she would run against Sen. Claire McCaskill (D-Mo.) in 2012 on Wednesday morning. McCaskill, first elected over Sen. Jim Talent (R) in 2006, is one of the most vulnerable incumbent Senators this cycle. Roll Call Politics rates this race as a Tossup.

Steelman’s announcement sounded like an appeal to the tea party groups who dominated Republican primaries across the country in 2010.

“We need to stop the frightening growth of government not only in size but in the power it holds over our lives by cutting government spending; balancing the budget; eliminating needless regulations; and reversing unwanted Obamacare mandates,” she wrote on SarahSteelman.com. “It means stopping the Washington elites from making America more like a European country instead of recognizing that people still flock to America because they know they can build a better life for their families.”

A former state Senator, Steelman served as treasurer from 2004 to 2008, when she lost the Republican primary for governor to Rep. Kenny Hulshof, who eventually lost to Democrat Jay Nixon. She considered running for the open Senate seat in 2010 but deferred to Rep. Roy Blunt, who ultimately won the seat vacated by retiring Sen. Kit Bond (R).

Talent is expected to announce whether he will seek a rematch with McCaskill in the first few months of 2011. It will be a big cycle for Missouri, as Nixon is also up for re-election and the state is on the cusp of losing a seat in the House in reapportionment.