By Brendan O'Brien
MADISON, Wis (Reuters) - Former Wisconsin governor Tommy Thompson officially launched his campaign on Thursday for the Senate seat being vacated by four-term Democratic Senator Herb Kohl.
Thompson, a Republican, served four terms as governor and then as Secretary of Health and Human Services in the George W. Bush administration. He joins a field for the Senate seat that currently includes Congresswoman Tammy Baldwin, a Democrat, and Republican Mark Neumann, a former congressman.
Wisconsin Assembly Speaker Jeff Fitzgerald, a Republican, is also vying for the seat. Fitzgerald was instrumental in passing controversial collective bargaining reform legislation in the state earlier this year.
Kohl, who has served since 1989, announced his retirement in May. Democrats in 2010 lost a long-time Senate seat held by the party when former Wisconsin Democratic Senator Russ Feingold was beaten by Republican challenger Ron Johnson. Feingold has decided not to run for any office in 2012.
Wisconsin is expected to be a major battleground in 2012, when Democratic President Barack Obama runs for re-election. If Republicans gain three seats in the 2012 Senate elections, the party could take over majority control of the upper chamber.
In announcing his candidacy, Thompson pledged to roll back big government regulations, implement free market solutions and create new jobs, according to his website.
"Our great nation is struggling with stubborn unemployment, record home foreclosures, business bankruptcies and failed leadership in Washington," he said in a letter to his supporters.
"I refuse to stand on the sidelines and let our children and grandchildren inherit a diminished nation that is less prosperous, less competitive and less free," he added.
Democratic Party of Wisconsin Chairman Mike Tate responded to the announcement by labeling Thompson as a "flip-flopping politician who will say whatever, whenever to whomever to get elected."
Tate took specific aim at Thompson's position on Obama's health care reform, which he promises to repeal if elected.
"Time and again, he defended the president and the common sense approach that eventually was enacted," Tate said in a conference call.
(Writing and reporting by Brendan O'Brien; Editing by Mary Wisniewski and Cynthia Johnston)