Former Sen. Russ Feingold (D-Wis.) has endorsed Rep. Tammy Baldwin (D) for Senate.

“Tammy is a true progressive champion, one of the strongest fighters for working families our state has ever produced and a hero to those of us who believe in breaking barriers and eliminating injustice in our society,” Feingold wrote in a post on her website and Facebook page.

Feingold, who lost his re-election bid last fall to GOP businessman Ron Johnson, has a strong following of liberal supporters. He resisted draft efforts to join the race when Sen. Herb Kohl (D) announced he would retire, and some of Feingold’s supporters hope he challenges Gov. Scott Walker (R) in a recall election next year.

Feingold also asked for donations to help Baldwin. “I’ll be proud to call her my Senator. Join me in supporting Tammy by making a contribution today to help her build her grass-roots campaign!” he wrote.