Manhattan Borough President Scott Stringer endorsed Sen. Kirsten Gillibrand (D-N.Y.) on Monday, months after mulling a possible primary challenge against her.

Stringer was one of a number of progressive New York Democrats who expressed interest in taking on Gillibrand, appointed to the seat in January, in a 2010 primary. He even went so far as to open an exploratory committee, only to drop his plans in May — in part, he said, because of the White House’s efforts to avoid a Democratic primary.

He did not mention Gillibrand in a statement announcing his decision not to run but did indirectly criticize some of the moderate positions that she had espoused as a Congresswoman.

Fast forward to December, when Stringer seems to be feeling a lot better about Gillibrand’s record.

In a statement announcing his endorsement, Stringer cited Gillibrand’s environmentally friendly initiatives, as well as her shift on gun control as reasons for his support. “Over the last year, Kirsten has truly impressed me and other City leaders with her fresh, smart approach to the problems we face,— he said.

Another outspoken progressive, Rep. Jerrold Nadler (D-N.Y.) endorsed Gillibrand last month. And a number of previously skeptical constituencies, including immigrant and gay rights groups as well as gun control advocates are now Gillibrand backers.

Several Democrats are still looking at a primary challenge to Gillibrand, but only labor activist Jonathan Tasini has officially announced a bid, and all of them would have an uphill climb, given the incumbent’s success at winning over her critics.

Former New York Mayor Rudy Giuliani, whom Republicans had hoped might challenge Gillibrand, signed on as a security advisor last week for the 2016 Olympics in Rio de Janeiro, prompting political wags in New York to conclude he is not focused on a 2010 run.