The US Senate rejected on Wednesday an effort to make any lifting of US sanctions on Iran part of an international nuclear agreement dependent on President Barack Obama certifying that Iran is not supporting acts of terrorism against Americans.
A handful of Republicans joined Senate Democrats to reject by a 54-45 vote a proposed amendment offered by Republican Senator John Barrasso that would have added the terrorism clause to a bill subjecting an international nuclear agreement to review by the US Congress.
The Senate has been engaged in intense debate over the legislation, a compromise version of the bill reached in the Senate Foreign Relations Committee last week in an effort to avoid a presidential veto.
A year-and-a-half before the 2016 election, presidential politics have also influenced the legislation.
Senators Bob Corker and Ben Cardin, the committee's Republican chairman and top Democrat, have been arguing against so-called poison pill amendments seeking to toughen the Iran Nuclear Review Act.
They insist those amendments would kill its chances of becoming law by alienating Democrats and provoking a veto. Obama considers tougher restrictions a threat to ongoing nuclear negotiations between Iran and six world powers.
Cardin had a heated exchange with Senator Marco Rubio, a Republican presidential hopeful, on Wednesday over one of the seven amendments Rubio has filed seeking to toughen the bill.
Rubio wants to amend the bill to prevent a nuclear deal from going forward unless Iran's leaders accept Israel's right to exist as a Jewish state, a measure certain to provoke a veto threat.
Rubio's critics have accused him of pushing the measure to enhance his foreign policy credentials as he fights for the White House. Pro-Israel politics are particularly important to evangelical Christian voters, a key part of the Republican base.
But Rubio accused some of his fellow senators of refusing to consider the amendment because they did not want to take a difficult vote.
Cardin, a Jewish lawmaker known as a strong supporter of Israel, vehemently disagreed and blasted the amendment as a poison pill. "It would make it almost impossible for the president to negotiate an agreement with Iran," he said.
The Barrasso amendment voted down on Wednesday sought to reinstate a clause that was removed last week as Democrats and Republicans worked out the compromise version of the bill.
Both of the amendments that have come up for a vote so far have been rejected.