Former Wisconsin Gov. Tommy Thompson (R) hasn't ruled out making a run for Senate next year, according to a spokesman.

Thompson joins a growing list of potential successors to Sen. Herb Kohl (D-Wis.), who announced Friday he wouldn't seek a fifth term. 

A spokesman for Thompson, contacted through the Washington law firm Akin Gump Strauss Hauer & Feld where he is a partner, said the former governor was "appreciative" of Kohl's service and " has not made any decisions" regarding a 2012 run.

In 2010, Thompson was considered such a strong contender against former Sen. Russ Feingold (D-Wis.) that National Republican Senatorial Committee Chairman John Cornyn (Texas) spoke to him about running. But despite poll numbers showing he'd be competitive, Thompson opted not to run against Feingold, who was subsequently defeated by Sen. Ron Johnson (R).

Feingold and GOP Rep. Paul Ryan both left open the possibility of a 2012 bid on Friday.

Thompson, who also served as a Bush Cabinet secretary, was briefly a candidate for president in 2008.