A bipartisan bill for Congress to review any nuclear agreement with Iran faced new danger Thursday as Republican senators sought to force votes on controversial amendments that leaders had hoped to avoid.
Senate Republican and Democratic leaders have worked all week to shield the bill from politically sensitive changes that are likely to drive away some Democratic supporters and sink its chances for passage.
Presidential campaign politics have complicated the process. One such amendment, from Sen. Marco Rubio (R-Fla.), a presidential candidate, would require Iran to recognize Israel's right to exist, something all senators would like to see, but that Iran is unlikely to do. The issue was not on the table during more than 10 years of negotiations over Iran's nuclear program.
But Republican senators pressed hard for their proposals, arguing that the legislation needed to be tough enough to protect U.S. and Israeli security.
Negotiators from the United States and five other world powers are seeking to complete a comprehensive deal with Tehran by June 30 that would lift sanctions on Iran if it accepts restrictions and inspections designed to prevent it from obtaining a nuclear weapon.
The Senate debate was interrupted Thursday as Sen. Tom Cotton (R-Ark.), in an unusual move, brought two amendments to the floor — including the amendment on Israel — over the wishes of lawmakers who have managed the deliberations.
Cotton said the proposals were not "poison pills," as critics claim, but "vitamin pills" that will strengthen the legislation.
The clash raised the possibility that Senate Majority Leader Mitch McConnell (R-Ky.) would need to shut down debate or withdraw the legislation for a few days, if not indefinitely.
"We're all balled up," said Sen. John Cornyn of Texas, the second-ranking Senate Republican.
He said that he hoped the legislation could move ahead but that "it's going to take a while for everybody to cool down."
The bill, sponsored by Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) and the committee's top Democrat, Sen. Benjamin L. Cardin (D-Md.), sets a procedure for Congress to review any nuclear agreement with Iran over a period of at least 30 days, and then vote on whether to lift economic sanctions that Congress has imposed on Iran.
The White House, which had previously threatened to veto legislation that would insert the Senate into the nuclear deal, backed down and agreed to support the proposed bill, which passed unanimously in the committee. President Obama has warned that he will veto the measure if it is revised in ways he believes could threaten the delicate negotiations.
Republican senators have proposed 67 amendments, including some politically sensitive ones that Democrats have been reluctant to vote against.
One Republican amendment, from Cotton, Rubio and fellow presidential candidate Sen. Ted Cruz (R-Texas) would require the United States to recognize Jerusalem as the capital of Israel, and to move the U.S. Embassy there from Tel Aviv. Washington considers Tel Aviv the capital under long-standing policy.
Democrats, who fear that such amendments are meant to sink the bill, are reluctant to allow votes on them unless GOP leaders agree that some Republicans will also vote against them. Otherwise, they worry that "no" votes could be used against them in future campaigns.
But negotiations have not yielded a deal on how to approach sensitive amendments. And the debate has put McConnell in an increasingly awkward position. He is wary of resisting fellow Republicans after promising "robust" deliberations over the legislation.
McConnell faces tough choices. He could call for a vote on the legislation without allowing further changes. That would probably allow the bill to advance, but it could anger colleagues who would be denied the chance to amend the bill.
It would also put McConnell in the politically uncomfortable position of relying on Democrats, rather than on fellow Republicans, to move legislation that the White House accepts on a national security priority.
He could also try to negotiate a deal to put forth fewer amendments.
If the Corker bill fails, other legislation would likely be proposed, but chances for passage would be dim. And it is not clear that tougher bills could attract enough Democratic support to override a presidential veto.
Some top Republican lawmakers, as well as diplomats from U.S. allies, have said privately that despite the unfolding drama over the bill, they doubt Congress will be able to stop or radically reshape the deal with Iran.