Capitol Hill
Capitol HillThinkstock

The United States Congress began tense deliberations Tuesday ahead of prospective votes on the Iran nuclear deal, as President Barack Obama gained sufficient Senate support to prevent Republicans' last-gasp efforts to torpedo his accord.

As lawmakers returned from summer recess, Senate Majority Leader Mitch McConnell said he would ask "all senators to be present in the chamber" to debate the merits and shortcomings of the international agreement aimed at preventing Iran from obtaining an atomic bomb.

Congress resumed just as the White House earned a major victory in securing support for the deal from 41 senators, the number needed to block a resolution disapproving of the controversial accord.

Should all 41 vote against advancing the Republican-backed resolution, a blocking procedure known as a filibuster, the effort to kill the landmark agreement would remain bogged down in the 100-member Senate.

The White House had launched an all-out effort to get lawmakers to back the international agreement that scales back Tehran's nuclear program in exchange for an easing of crippling economic sanctions.

Despite a Republican-driven lobbying push against the accord, Obama last month had won enough support to sustain the veto he would lodge if Congress were to disapprove of the deal.

Four Senate Democrats stand opposed to the agreement, including Chuck Schumer, who is expected to be the next Democratic leader in 2017. Also opposed are New Jersey's Bob Menendez and Maryland’s Ben Cardin.

The House of Representatives is expected to vote on its resolution of disapproval later this week.

But with Senators Ron Wyden, Gary Peters and Richard Blumenthal joining Obama's nuclear deal camp Tuesday, there are enough votes to prevent the resolution from advancing in the Senate.

Some Democrats, including Senator Chris Coons, are reportedly suggesting they would prefer a direct up-or-down vote on the resolution instead of blocking it.

McConnell sought a final vote as well, and called on "every senator to resist attempts to obstruct a final vote and deny the American people and Congress the say they deserve on this important issue."

In his effort to derail the accord, McConnell warned that "by almost any measure, we know that Iran will emerge stronger from this deal in nearly every aspect of its national power, and better positioned to expand its sphere of influence."

McConnell admitted last month that it would be unlikely that Congress will be able to block the Iran nuclear deal, despite a Republican majority in both houses, saying Obama has "a great likelihood of success" in pushing the deal through.

Many Democrats backing the deal have done so reluctantly or with skepticism, particularly due to what Wyden on Tuesday called "the history of Iran's deception."

"This agreement with the duplicitous and untrustworthy Iranian regime falls short of what I had envisioned, however I have decided the alternatives are even more dangerous," Wyden said.

Meanwhile, Republican former vice president Dick Cheney blasted the deal as "madness" and "capitulation" to Iran.

"Every member of Congress swears to defend the Constitution from enemies outside our shores," Cheney said Tuesday as the American Enterprise Institute, a conservative think tank in Washington.

"A vote to reject that agreement will do that. Approving it will not."

AFP contributed to this report.