FILE PHOTO: Former Rep. Beto O'Rourke speaks before a Democratic Party fundraising dinner, the Liberty and Justice Celebration, in Des Moines, Iowa, U.S. November 1, 2019. REUTERS/Eric Thayer

DALLAS (Reuters) - Former Texas Congressman Beto O’Rourke endorsed former Vice President Joe Biden for Democrats’ presidential nomination, as moderate Democrats rallied around the former vice president to strengthen his challenge to front-runner Bernie Sanders.