Zuckerman said personal and political reasons motivated his decision not to run.
Zuckerman was mentioned as a potential opponent of Sen. Kirsten GillibrandKirsten GillibrandDems separated by 29 votes in NY House primary Former Gillibrand aide wins NY House primary Dems celebrate anniversary of gay marriage ruling MORE (D-N.Y.) in this fall's midterms. The billionaire real estate mogul and owner of the U.S. News did not rule out a run two weekends ago amidst rumors he would run as an independent or Republican candidate.
It's the second time this week Gillibrand has lost a potential, high- profile challenger. Former Rep. Harold Ford, Jr. (D-Tenn.) announced this week he would not primary the appointed senator.
Democrats acknowledged Gillibrand's positives just after the Zuckerman announcement was made public. Gillibrand has suffered from low polling numbers and name recognition, which invited potential challengers.
"In just a short time, Senator Gillibrand has proven herself to be an effective fighter for New York," Democratic Senatorial Campaign Committee Chairman Robert MenendezRobert MenendezOvernight Finance: Trump threatens NAFTA withdrawal | Senate poised for crucial Puerto Rico vote | Ryan calls for UK trade deal | Senate Dems block Zika funding deal Menendez rails against Puerto Rico bill for 4 hours on floor Overnight Cybersecurity: Senate narrowly rejects expanding FBI surveillance powers MORE (D-N.J.) in a statement. "She's working hard, getting around the state, building coalitions of support - including some who were initially skeptical upon her appointment. But as we have seen time and time again, she is New York tough and she is impressing New Yorkers every chance she gets."