The decision by Ms. Ramos, a state senator from Queens, is at odds with her frequent criticism of Andrew M. Cuomo, including comments questioning his “mental acuity.”

Cuomo’s bid for New York City mayor got a jolt of momentum when Jessica Ramos, who spent months torching Cuomo’s character, endorsed him.

Andrew Cuomo faced a two-hour pile-on Wednesday as eight other Democrats vying for the party’s nomination for New York City mayor spent their first debate attempting to knock the former governor off his perch.