The international nuclear accord with Iran will be center stage in Congress when lawmakers return from a month-long recess next week and almost immediately launch into what promises to be passionate and rancorous debate on a pact that has enormous implications for U.S. and global security.

President Barack Obama has secured enough Democratic support for the deal to sustain a promised veto of any resolution of disapproval from the Republican-led legislature, but not enough to block such a measure from reaching his desk.

From the moment the deal’s provisions were unveiled, leaders of both houses of Congress pledged to block it under a law passed earlier this year granting lawmakers the ability to review and vote on the nuclear accord.

“We’ll do everything we can to stop it,” said House Speaker John Boehner.

“I think it is going to be a hard sell. Hard sell,” said Senate Majority Leader Mitch McConnell on Fox News Sunday.

Sen. Chris Coons D-Del., accompanied by his wife A
Sen. Chris Coons D-Del., accompanied by his wife Annie, left, and family, speaks to supporters after winning his re-election bid for the Senate, Tuesday, Nov. 4, 2014, during election night party in Newark, Del.

Veto override

But blocking the pact would require Congress to override a presidential veto. As of this week, enough Democrats have announced their support to ensure the veto is sustained in the Senate and the accord goes into effect.

“I am voting for this agreement because it is our most credible opportunity to lead a global community in containing an existential threat,” said Senator Chris Coons, one of several Democrats who have come out in favor of the accord in recent days.

Even so, the deal has exposed Congress’ ever-present partisan fault lines.

“It is possible, and indeed likely, that the Iran nuclear agreement will receive no Republican votes whatsoever in Congress,” said former U.S. Ambassador Norman Eisen, currently a scholar at the Washington-based Brookings Institution.

Some deal backers hope to avoid Senate action altogether, but currently lack the votes to block consideration of a resolution of disapproval.

Senator Bob Corker speaks to reports at the US Cap
Senator Bob Corker speaks to reporters at the US Capitol in Washington, April 21, 2015.

Effort to silence Congress

Key Republicans are dismayed by what they see as an effort to silence Congress.

“There is perhaps no greater geo-political issue facing the world today than preventing a nuclear-armed Iran. And so we owe it to the American people to have a thorough and thoughtful debate,” said Senator Bob Corker, chairman of the Senate Foreign Relations Committee.

Others see value in avoiding an exercise that exposes domestic political divisions on a major international accord.

“There is a logic to preventing cloture, to blocking the vote, because it is pointless – why set up a great drama when the agreement is going to go through anyhow?” said Eisen.

Some lawmakers have yet to announce a position, including the top Democrat on the Senate Foreign Relations Committee, Ben Cardin.

“This is one of the more difficult decisions that Congress – and I – have made. It’s one that evokes a great deal of emotion,” said Cardin.

A vote in the House of Representatives could come as early as next week.