WASHINGTON – In a Senate hearing on Tuesday, Foreign Relations Committee chairman Robert Menendez challenged US President Barack Obama on the weight of his vow to seek new sanctions against Iran should talks over its nuclear program fail.Questioning Wendy Sherman, the chief US negotiator, Menendez (D-New Jersey) noted that Iran’s continued nuclear-related research and development would shorten the window of time required by the Islamic Republic to produce a nuclear weapon – even as negotiations take place. “In reality, the only effect we have is over time,” Menendez said. “To enforce sanctions then would be far beyond the scope or the window.”“It’s not simply about passing sanctions,” he added. “It’s about the time frame necessary to have them be effective.”In his State of the Union address on January 28, the president said he would be the first man in Washington to call for new sanctions if Iran fails to agree to a comprehensive nuclear accord satisfactory to the US and its allies.In the same speech, he promised to veto any new sanctions legislation that might compromise the diplomatic process. Menendez introduced just such a bill in December that he described as an “insurance policy” for Congress. That bill has garnered 59 co-sponsors across party lines.Midway through Tuesday’s hearing, Menendez pushed back against the Obama administration for referring to his strategy as tantamount to a “march to war,” a phrase Jay Carney, the White House press secretary, used several times after the bill’s rollout.“I don’t believe any of you, any senator, any member of the House are warmongers. I don’t believe anyone prefers war,” Sherman agreed. “Tactical considerations may lead us to that choice. But that is an issue of tactics, not an issue of intent.”Sherman conditioned her testimony by noting that she would not negotiate with Iran in public. But she said that Tehran’s scientists “cannot unlearn what they know” about nuclear weaponry, and that the US delegation was focused instead on preventing Iran from being physically able to build such a weapon.“The coming months will be a test of Iran’s intentions,” she said.Sherman defended the short-term nuclear agreement, reached in Geneva in November between Iran and world powers, a negotiation she led personally.“This is not perfect,” she said, referring to the six-month pause that began on January 20, known formally as the Joint Plan of Action.“But we agreed on a six-month program that freezes where they are, and rolls back their program in significant ways.”The US would be willing to tolerate a “small, limited enrichment program,” Sherman added – a position that Prime Minister Binyamin Netanyahu vehemently opposes.Menendez asked the diplomat to comment on recent statements by Iranian leaders, including President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif, that the Islamic Republic would never dismantle its extensive centrifuge program.“It is their maximalist negotiating position,” Sherman said, chalking up the comments to political talk for domestic consumption. “I wouldn’t expect any less.”Also testifying was David S. Cohen, under secretary for terrorism and financial intelligence at the US Treasury Department, who repeated the administration’s assertions that most sanctions against Iran would be vigorously enforced.But Sen. Jeanne Shaheen (D-New Hampshire) asked Cohen whether European allies would comply just as well, noting that “expansive EU trade delegations” were preparing to travel to Tehran to explore newfound business opportunities.“If these talks turn into deals that violate the elaborate sanctions we have in place, then we’ll take action,” Cohen said, repeating that Iran “is not open for business.”The ranking member of the committee, Sen. Bob Corker (R-Tennessee), said he was concerned that the interim agreement would gel into a new status quo.“Somehow, because Congress wants to ensure that we end up with a proper end state, there’s been a lot of unfortunate things that have been said,” Corker said, calling for continued pressure from his colleagues.Corker is a strong supporter of Menendez’s bill, the Nuclear Weapon Free Iran Act of 2013, which would trigger new sanctions tools against Iran if a deal is not reached in one year.In his opening remarks, Menendez tacitly conceded that Iran is already a nuclear- threshold state.“If all we achieve is the essence of an early-warning system in Iran’s future breakout ability, and the sanctions regime has collapsed, and the only options for this or any future president is to accept a nuclear-armed Iran or a military option, in my view, that is not in the national security interests of the United States,” Menendez said.“I know that is not anyone’s goal or plan, but I also think we need to guard against wanting a deal so much that we concede more than we gain,” he said.