Former Wisconsin Senator Russ Feingold on Wednesday endorsed the candidacy of Tammy Baldwin for U.S. Senate, gay weekly The Washington Blade reported.

Baldwin is running for the Senate seat being vacated by Wisconsin Senator Herb Kohl.

“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 said in an email to supporters. “I was proud to call her a colleague as we fought together in Washington for Wisconsin families — and I'll be proud to call her my senator.”

The Wisconsin Rep. is the first and so far only Democrat to formally declare her candidacy for the seat.

Former Wisconsin Governor Tommy Thompson, former Rep. Mark Neumann and Wisconsin Assembly Speaker Jeff Fitzgerald are vying for the GOP nomination.

If elected, Baldwin would become the first openly gay person to serve in the Senate. However, she has already said that her candidacy would not be about her sexual orientation.