The Disclose Act, a bill that would force corporations, unions, and other groups to reveal the donors behind their political advertisements, was not to be. On Tuesday, Senate Democrats were three votes short of the 60 needed to stop a filibuster, thus ending any chance, for now, that there could be new disclosure requirements for the 2010 elections. The vote, which represents a significant setback for President Obama and the Democratic Party, is a big win for Senate Republicans and business groups. The legislation would impose stricter financial-disclosure requirements and would restrict political activity for companies with federal contracts of more than $10 million or TARP funds. The act was introduced after the Supreme Court ruled in January in favor of unlimited corporate spending for elections.