Sen. Kirsten Gillibrand (D-N.Y.) continued to consolidate progressive support Monday when prospective primary challenger Jon Cooper (D), the Suffolk County Legislative majority leader, not only announced he would not run but threw his support behind the senator.

“I’ve always said that my decision would ultimately be based on what’s best for the Democratic Party, New York State and our nation,” Cooper said in a speech in Mineola, N.Y., offering Gillibrand his “wholehearted endorsement.”

The openly gay legislator had been exploring a campaign since last spring. He was unlikely to give Gillibrand a major scare, but he could have marshaled grassroots support thanks to his time as an Obama organizer during the 2008 presidential campaign and his ties to the local progressive community.

He told CQ-Roll Call that since his announcement he has been overwhelmed with responses from supporters saying he would now back Gillibrand.