Former Rep. Mark Neumann, R-Wis., plans to enter the race for retiring Democratic Sen. Herb Kohl's seat, according to a source familiar with the former congressman's plans.
The source said Neumann is expected to make his official announcement as early as next Monday.
This will be the second Senate run for Neumann, who served in the House from 1995-1999. He lost a challenge to Democrat Russ Feingold in 1998. Most recently, Neumann ran for governor in 2010, losing in the GOP primary to now-Gov. Scott Walker.
Neumann is expected to run to the right of former Gov. Tommy Thompson, who is also preparing to make a Senate bid. The fiscally-conservative Club For Growth has been actively opposing a Thompson candidacy, and the group has even run a television ad tying Thompson to President Obama. It's not clear yet whether the Club will get behind Neumann in the race, though he has expressed hope that the organization will. The group's executive vice president is a former Neumann aide.
One of Neumann's strengths is his ability to self-fund. He spent over $6 million in the governor's race, much of which was his own money. Despite spending heavily, he still got blown out by Walker. But many conservatives will no doubt be excited about having a viable alternative to Thompson.
Other possible Republican candidates include former state Sen. Ted Kanavas and state Assembly Speaker Jeff Fitzgerald. On the Democratic side, Rep. Tammy Baldwin, who is likely to make a bid of her own, is the early frontrunner.