Johnson stunned the nation on March 31 when he withdrew from the race and four weeks later his Vice President Hubert H. Humphrey, entered the race, though he did not run in any primary. Kennedy and McCarthy traded primary victories while Humphrey gathered the support of labor unions and the big-city bosses. Kennedy won the critical California primary on June 4, but he was assassinated that night. Even as Kennedy won California, Humphrey had already amassed 1,000 of the 1,312 delegate votes needed for the nomination, while Kennedy had about 700.