WASHINGTON — After having come tantalizingly close over the weekend to an agreement to freeze Iran’s nuclear program , the Obama administration is gingerly weighing a threat to the talks potentially more troublesome than the opaque leadership in Tehran: Congress. Secretary of State John Kerry will meet behind closed doors on Wednesday afternoon with members of the Senate Banking, Housing and Urban Affairs Committee to try to head off a new round of stiff sanctions on Iran that administration officials fear could derail the talks in Geneva. In addition, Vice President Joseph R. Biden Jr.; Mr. Kerry; Wendy R. Sherman, the administration’s chief negotiator; and David S. Cohen, under secretary of the Treasury for terrorism and financial intelligence, are scheduled to brief Senate Democratic leaders that day in a full-court press to win backing of the diplomatic initiative. But the administration is running headlong into Prime Minister Benjamin Netanyahu […]