[...] as Obama tries to rally Democrats around the chief economic proposal of his second term, the party's presidential front-runner has stayed conspicuously silent. [...] that negotiations have concluded, Clinton soon will be forced to choose between supporting the president on a legacy-enhancing issue or siding with labor unions, environmentalists and other liberal constituencies that oppose the deal. Clinton's campaign and the Obama administration have always said the time would come when she would outline her own policies and deliver criticisms, implied and direct, of Obama. Clinton's main challenger, Vermont Sen.