Zuckerman said personal and political reasons motivated his decision not to run.
Zuckerman was mentioned as a potential opponent of Sen. Kirsten Gillibrand (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 Menendez (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."