Cory booker joe biden endorsed by another ex rival

You're referring to the 2020 Democratic presidential primary!

Yes, you're correct. After Joe Biden and Cory Booker were rivals in the primary, Booker endorsed Biden for president in April 2020. Booker, a U.S. Senator from New Jersey, was one of the many candidates who dropped out of the race before the Iowa caucuses, and he later threw his support behind Biden's campaign.

Booker's endorsement was significant because he was one of the few African American candidates who ran in the primary, and his endorsement helped to boost Biden's credibility with African American voters.