Negotiators of Iran and six world powers face each other at a table in the historic basement of Palais Coburg hotel in Vienna.

Senate Majority Leader Mitch McConnell set a test vote for Thursday on stalled bipartisan legislation to let Congress review and possibly reject any agreement the Obama administration makes to ease sanctions on Iran in exchange for concessions on nuclear research and development.

The bill has been on the Senate floor off and on for more than two weeks.

It has been stalled since Republican Sens. Marco Rubio of Florida and Tom Cotton of Arkansas proposed politically attractive changes that drew the objections of Democrats as well as some Republicans who want the bill kept free of controversial provisions that could prompt the White House to withdraw its support.

A 60-vote majority on Thursday’s test vote would likely jettison both proposals, and greatly improve the bill’s chances of passage.

Supporters want the bill passed free of controversial add-ons they claim could scuttle negotiations with Tehran, draw a presidential veto or leave lawmakers with no say on a national security threat. Negotiators for the U.S. and five other nations are rushing toward a June 30 deadline to finalize a deal in which Iran would curb its nuclear program in exchange for relief from sanctions choking its economy.

Rubio, who is running for president, wants to amend the bill to require Iran’s leaders to publicly accept Israel’s right to exist, a nearly impossible mandate.

Cotton’s proposal says that before sanctions could be lifted on Iran, President Barack Obama has to certify that the country is not engaging in acts of terror against America or Americans.

Cotton blamed Democrats for not allowing his amendment to be voted on the floor.

“Congress must stand up and protect (the) U.S. from a nuclear Iran. It’s regrettable that Democratic intransigence blocked efforts to strengthen this bill,” Cotton tweeted.

Other Republicans have proposed changes to the measure that do not appear to be as controversial, and it is not clear what their fate would be if supporters can amass 60 votes on Thursday to limit debate. Other Republicans want to require Iran to release four prisoners before sanctions are lifted.

As written, the legislation would block President Barack Obama from waiving congressional sanctions for at least 30 days while lawmakers weigh in on any final deal the U.S. and five other nations can reach with Iran. It also would stipulate that if senators disapprove the deal, Obama would lose the current authority he holds to waive certain economic penalties Congress has imposed on Iran.

The bill has gained tacit approval from Obama. He says he will sign it as written, but the White House warns that he will reconsider if the measure is substantially changed. More than 60 amendments have been proposed.

Sen. Bob Corker, a lead sponsor of the bill and chairman of the Senate Foreign Relations Committee, predicted that the bill could pass the Senate with more than 90 votes.

“I think if we get the final vote without additional blow-ups between now and then, I think it’s going to be overwhelming,” Corker said after McConnell announced the test vote.

He said he thinks there is a possibility that a half dozen or more non-controversial – ones Corker said were meant to strengthen the bill – could still be incorporated in the final measure.

Democratic Sen. Tim Kaine, a member of the committee, said Republicans should want the bill to pass because if it doesn’t, the president can unilaterally decide – without any check from Congress – to waive or suspend sanctions imposed by Congress. If the bill was loaded with controversial amendments, Democratic support would waiver.

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