(AP) — Former President Barack Obama endorsed U.S. Sen. Dianne Feinstein on Friday, wading into her re-election fight against a fellow Democrat.

He urged Californians to return “one of America’s most effective champions for progress to the Senate,” in a statement released by Feinstein’s campaign.

Feinstein is seeking her fifth full term in Washington. She’s facing a challenge from state Sen. Kevin de Leon, who argues she hasn’t done enough to stand up to President Donald Trump. The state’s June 5 primary will send the two highest vote getters to the general election, regardless of party. No prominent Republicans are running, opening the path for a contest between Democrats.

De Leon’s campaign didn’t immediately comment on Obama’s endorsement, but announced backing from Spanish-language newspaper La Opinion.

Obama and Feinstein have worked together for a dozen years, first during his brief time in the U.S. Senate then during his presidency. Feinstein supported Hillary Clinton in the 2008 presidential primary, and after Obama secured the nomination Feinstein lent the two her Washington, D.C., home for a brief meeting.

Feinstein later served as the chair of Obama’s first inaugural ceremony.

Obama, in his statement, cited their work together on affordable health care, climate change and gun control.