McConnell threatens to bring Israel amendment into Iran debate
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"I will file on an amendment that would prevent the president from lifting sanctions until Iran meets two simple benchmarks," McConnell said. "It must formally recognize Israel’s right to exist, and it must release the American citizens being held in Iranian custody." 
The Republican leader's remarks come ahead of a second vote on moving forward with a resolution of disapproval on the Iran nuclear deal. Democrats are expected to block the resolution, as they did last week.
A spokesman for McConnell added that if Democrats don't allow a vote on the Iran resolution, the Republican leader will file cloture on the amendment, forcing a procedural vote later this week. 
Key Democrats who support the deal, as well as the Obama administration, have argued that the Iran debate should be focused only on the country's nuclear program, and not other contentious areas including the country's support for terrorism. 
McConnell, however, said linking the issues is "appropriate." 

"My strong preference is for Democrats to simply allow an up-or-down vote on the president’s Iran deal," he added. “But if they’re determined to make that impossible, then at the very least we should be able to provide some protection to Israel and long-overdue relief to Americans who’ve languished in Iranian custody for years." 

McConnell's move could put Democrats in a tough spot.

A push by Sens. Marco RubioMarco Antonio RubioLiberal super PAC launches browser extension replacing 'Mitch McConnell' with 'Moscow Mitch' Trump faces difficult balancing act with reelection campaign Republicans wary of US action on Iran MORE (R-Fla.) and Tom CottonThomas (Tom) Bryant CottonZuckerberg woos Washington critics during visit Zuckerberg to meet with lawmakers to discuss 'future internet regulation' 2020 Democrats raise alarm about China's intellectual property theft MORE (R-Ark.) to force a vote on requiring Iran to publicly recognize Israel effectively shut down the debate over the review bill earlier this year.

Separate amendments calling for Iran to release three Americans currently held in the country were also never allowed to come up for a vote. Democrats warned that the amendments were "poison pills" designed to kill the nuclear agreement.

Democrats have argued that it's time for the Senate to move on to other issues, including how to fund the government. But McConnell warned that the debate "will continue. This is an issue with a very, very long shelf life."  

Senate Minority Leader Harry ReidHarry Mason ReidBarr fails to persuade Cruz on expanded background checks Harry Reid warns Trump 'can be reelected' Homeland Security Republican accuses Navy of withholding UFO info MORE (D-Nev.) ripped Republicans ahead of the vote, reiterating his offer to allow the Senate to skip to final passage of the resolution as long as the threshold is set at 60 votes.

"It is hard for me to comprehend how my Republican colleagues, with a straight face, can talk about let's have an up-or-down vote on this," he added. "We agreed to allow Republicans to have an up-or-down vote."

McConnell has been under pressure from conservatives in the House, as well as Sen. Ted CruzRafael (Ted) Edward CruzState Department's top arms control official leaving Sanders NASA plan is definitely Earth first Trump judicial picks face rare GOP opposition MORE (R-Texas), to take a more aggressive approach to stopping the Iran agreement.

House Republicans wanted him to use the "nuclear option," while Cruz—who is running for president—wanted him to say that the congressional review period for the Iran deal hasn't started because the administration didn't hand over "side deals" between Iran and the International Atomic Energy Agency (IAEA).

— This story was updated at 6:48 p.m.