Mayor Jim Kenney is backing Massachusetts Sen. Elizabeth Warren in the 2020 Democratic primary race for president, becoming the first big-city mayor to endorse her.

Kenney announced his endorsement Wednesday in an early morning email.

“This is a critical election that will determine our nation’s future and our priorities. Elizabeth Warren is a tough and determined leader,” it said. “Elizabeth Warren and I share a progressive Democratic agenda. She’ll focus on equality and equity of opportunity, lasting job creation, serious criminal justice reform, child care and pre-K education — along with secondary and post-secondary educational improvements and opportunities for all our children."

For Warren, the nod is a show of support in a city where one of her biggest rivals, former Vice President Joe Biden, has deep political ties and has situated his campaign headquarters. Biden has far outpaced his rivals in endorsements from elected Democrats in Pennsylvania.

Fellow Democrats Sen. Bob Casey of Pennsylvania and U.S. Reps. Dwight Evans and Brendan Boyle, who represent parts of Philadelphia, have endorsed Biden. Biden campaigned in Scranton, the city of his birth, on Wednesday.

Overall, Warren trails Biden and Sens. Cory Booker of New Jersey and Kamala Harris of California in the FiveThirtyEight endorsement tracker. The Working Families Party, a progressive group active in Philadelphia, backed Warren this summer.

Kenney’s endorsement comes about a week after New York Rep. Alexandria Ocasio-Cortez announced her backing of Sen. Bernie Sanders.

Warren said in a statement: “I’m honored to have Mayor Kenney’s support. He’s been a champion for working families in Philadelphia. With the mayor’s support, we can win in 2020 and make the big structural change we need so our government, our economy, and our country works for every person, not just the wealthy and well-connected.”