Joe Biden’s allies are becoming increasingly concerned that a Mike Bloomberg candidacy could take votes away from the former vice president and help Sen. Elizabeth Warren win the race for the Democratic presidential nomination.

Bloomberg’s political aides confirmed that he’s again considering entering the 2020 race, after he decided against it in March. Top Bloomberg advisor Howard Wolfson said Thursday that the billionaire former New York mayor is “increasingly concerned that the current field of candidates is not well-positioned” to defeat President Donald Trump next year.

Biden told reporters on Friday that he welcomes Bloomberg, a fellow moderate, into the race. Yet several of his supporters see the former mayor’s move as potentially giving an edge to Warren, a liberal populist.

“This hurts Biden tremendously,” said one of Gov. Andrew Cuomo’s outside advisors. Cuomo has encouraged his vast donor network to back the former vice president. “Even if he doesn’t get it,” this person added, “the whole thing plays that Biden is weak. It cements in people’s minds that Biden can’t make it work.”