"We've seen this strategy before, it never works," the Democratic leader said. "If the Republican leader has his way, all the Senate will do for the rest of this week is take yet another failed vote on Iran."

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Senate Democrats blocked a resolution for disapproving the Iran nuclear agreement from getting the 60 votes it needed to move forward on Tuesday.

If Democrats block the amendment, which will need 60 votes to overcome a procedural hurdle, it will be the second time they blocked Republicans on Iran this week.

But McConnell's amendment could be a politically tough vote for Democrats on a deal that has divided Americans.

According to a CNN/ORC poll released Sunday, nearly half of Americans thought Congress should reject the deal.

Separate amendments on demanding that Iran release Americans currently in the country also weren't allowed to come up for a vote.

Democrats, and some Republicans, acknowledged at the time that the amendments would either kill the review bill or derail the Iran deal, which was still being negotiated.

Despite McConnell's latest maneuver, the deal is all but guaranteed to survive Congress, handing Obama a major foreign policy victory.

Reid acknowledged as much on Wednesday, saying that no matter Republicans "future plans, it will not prevent President Obama and his administration from implementing the Iran agreement."