New Jersey Sen. Cory Booker, a new entrant in the Democratic presidential fray, on Friday cast doubt on former Starbucks CEO Howard Schultz’s chances in the 2020 field, saying independent candidates “don’t win” presidential races.

“I’m obviously not happy — we know the history of what independents do,” Booker told radio host Joe Madison Friday morning after announcing his 2020 bid. “They don’t win, and they end up often tearing down the progressive candidate, the Democratic candidate.”