WASHINGTON (AP) — Senate Republicans labored Monday to salvage bipartisan legislation granting lawmakers the right to review or even reject any agreement the Obama administration makes to ease sanctions on Iran in exchange for concessions on nuclear research and development.

Officials said Majority Leader Mitch McConnell, R-Ky., hoped to avoid staging a showdown vote to limit debate on the measure, a move that could split his own party's rank and file.

Democrats urged him to go ahead anyway, as a way to avoid votes on proposed changes they opposed. "It's the only path forward to pass this meritorious legislation," said the party's leader, Sen. Harry Reid of Nevada.

McConnell declined to comment on what he planned to do on the Iran bill, brushing off the question posed by reporters as he walked to the floor vote.

The legislation was approved by the Senate Foreign Relations Committee on a unanimous vote last month, and supporters easily turned back a pair of proposed changes in early skirmishes on the Senate floor.

But the measure hit a snag last week after Sens. Marco Rubio, R-Fla., and Tom Cotton, R-Ark., proposed additional changes that drew strong objections from Senate Democrats, as well as from Republicans who favor keeping the bill free of controversial provisions that could prompt the White House to withdraw its support.

Rubio, an announced presidential candidate, wants to require Iranian leaders to recognize the right of Israel to exist before an agreement can be put into effect.

Since Iran is committed to the destruction of Israel, the proposal is widely viewed as an attempt to scuttle any agreement with Tehran. At the same time, Democrats who are sympathetic to the negotiations with Iran would have a difficult time opposing the Israel-related proposal because of domestic politics.

Asked if he favored Rubio's amendment, Sen. John McCain, R-Ariz., said: "Spiritually, yes. But would I vote for it? No. Because the Democrats say they'd walk and if the Democrats walk, we're back to square one."

Cotton's amendment would require Obama to certify that Iran was not sponsoring acts of terror against America or its citizens before an agreement could take effect.

Maryland Sen. Ben Cardin, the ranking Democrat on the Senate Foreign Relations Committee, denounced the Rubio and Cotton amendments.

"They are what we call 'poison pills' and so one of three things would happen: The bill doesn't make it to the finish line," he said. "It derails negotiations and the U.S. is blamed for the failure of negotiations with that consequence. Or, it makes negotiations virtually impossible to get the strongest possible deal."

As drafted, the legislation would block 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 reach with Iran. The White House backs the measure in its current form.

It would take a separate piece of legislation for Congress to block implementation of any deal. Even if lawmakers were to approve a bill along those lines, the president could veto it.