This summer, the US Senate will choose between war and peace with Iran. If the right decision is made, Obama’s pending nuclear deal with Iran will be sustained and both a war and an Iranian nuclear bomb will be avoided. If the wrong vote is cast, diplomacy will collapse and the US and Iran will once again be on a path towards a disastrous war that will make the Iraq war look like the cake-walk it was promised to be. The good news is: If Americans speak up in large numbers, the Senate will choose peace.

This crucial vote will likely take place in July after a deal has been reached and before Congress leaves town for the summer recess. It’s the result of the Senate passing the Iran Nuclear Agreement Review Act 98-1 this past Thursday. The House is expected to take up the legislation as soon as this week, and the President will sign it into law thereafter — assuming no “poison pill” amendments are inserted.

In essence, the bill restricts the President’s authorities to waive sanctions while Congress considers whether or not to reject an agreement. A vote of disapproval would permanently revoke the President’s authorities to offer substantial sanctions relief and thus block the US from implementing the deal. If Congressional hawks were to succeed in blocking a deal that our negotiators had agreed to, it would not just set a devastating precedent for any future US diplomatic efforts, it would unravel nuclear constraints and international sanctions on Iran and put war on the front burner.

A vote of disapproval would require 60 votes to pass the Senate and a simple majority to pass the House. If supporters of peace lose this vote, the president will have no choice but to veto the resolution. The other side will then seek to override Obama’s veto – and for that they will need two-thirds of both the Senate and House, i.e. 67 Senators and 290 Representatives.

That’s the vote that the American people cannot afford to lose.

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At the moment, it appears that supporters of a deal have sufficient numbers to uphold a veto and protect the deal. At the same time that the Senate passed the review bill, 151 Democrats in the House of Representatives sent a letter to the President commending the framework nuclear agreement and urging that our diplomats seal a final deal. Given that the letter was signed by more than a third of the House, if the same number of representatives refuse to reject a final deal, a Presidential veto would hold. That letter, led by Reps. Jan Schakowsky (D-IL), Lloyd Doggett (D-TX) and David Price (D-NC), will undoubtedly boost perceptions in Iran that President Obama can uphold America’s end of the nuclear bargain.

However, nothing is certain — especially for a showdown vote that powerful interest groups like AIPAC have been preparing for over a decade, according to a former lobbyist from the organization . Furthermore, if the President is only able to protect a deal by veto, it could encourage opponents to cry foul and pursue additional efforts to block and undermine the deal. Unless the attempt to kill an agreement is soundly defeated this summer, there could be further efforts to re-litigate the deal in Congress, limit the President from implementing it, and pass new sanctions to kill the agreement.

The endgame is now fast approaching. Iran and the United States will likely convert their agreement in principle into a historic deal this summer. Then, Congress will take a critical vote to determine whether the U.S. continues down the path toward peace or marches down the road to war. If accepted, it can be the beginning of the end of more than three and a half decades of US-Iran enmity. In the weeks ahead, it is imperative that the American people make sure that Congress ends up on the right side of history.

This piece originally appeared in The Huffington Post.