US Senate Democrats have blocked a resolution against the Iran agreement for a third time in a week, sealing a major foreign policy victory for President Barack Obama.

As was expected, the Republicans failed once again on Thursday to gather the 60 votes needed for the resolution of disapproval in the 100-member chamber.

Fifty-six of Republican senators voted against ending debate on the resolution of disapproval.

Republican Senators Rand Paul of Kentucky and Marco Rubio of Florida missed the vote, while Senators Ted Cruz of Texas and Lindsey Graham of South Carolina voted with every other Senate Republican to advance the resolution.

All four senators are seeking Republican nomination and participated in the second GOP presidential debate on Wednesday night in California.

Four Democratic senators for a third time betrayed Obama, voting against the Joint Comprehensive Plan of Action (JCPOA) reached between Iran and the P5+1 group of countries.

They are Chuck Schumer of New York, Ben Cardin of Maryland, Senator Joe Manchin of West Virginia and Bob Menendez of New Jersey.

Under the Iran Nuclear Agreement Review Act, which gave Congress the power to review the Iran deal, Thursday is the final day for Congress to disapprove of the nuclear deal.

Thursday's vote comes after Democrats previously blocked the resolution of disapproval from moving forward twice in the Senate.

With neither chamber of Congress expected to go for another vote on the Iran nuclear agreement, the Obama administration is certain to save the agreement after months of intense lobbying efforts.

This means the legislation aimed at sabotaging the historic agreement is essentially dead, and that the deal will now take effect without a veto showdown between the Republican-controlled Congress and the Obama administration.

Opponents of the Vienna nuclear accord appeared to acknowledge defeat ahead of Thursday's vote.

"This agreement is moving forward, we all know that," said Cardin, the ranking member of the Foreign Relations Committee.

GOP Senator Bob Corker said that Republicans understand that "42 senators are causing a filibuster to take place and that we're not every going to be able to get to that vote on conscience.”

The Obama administration has gained this resounding victory over its opponents, despite the Israel lobby’s massive campaign to defeat the historic nuclear agreement, reached between Iran and the P5+1 -- the US, Britain, Russia, China, France, and Germany -- in Vienna in mid-July.