Bob Casey

WASHINGTON — President Barack Obama is just one Senate vote shy of being able to declare success on the Iran nuclear deal and cement a foreign policy legacy.

Senate support for the deal now stands at 33 votes, thanks to announcements Tuesday from Democrats Bob Casey of Pennsylvania and Chris Coons of Delaware.

Once supporters reach 34 votes, they would be able to uphold Obama’s expected veto of GOP legislation aimed at blocking the Iran deal. That disapproval resolution is set for a vote later this month.

Secretary of State John Kerry is sending a letter to all members of Congress outlining U.S. security commitments to Israel and the Gulf Arab states in light of the nuclear deal. The letter comes as Kerry prepares to deliver a major policy speech Wednesday in Philadelphia that focuses on how the international agreement makes the U.S. and its allies safer and how the deal is being mischaracterized by some opponents.

“I really believe the fastest way to a genuine arms race in the Middle East is to not have this agreement,” Kerry said in a nationally broadcast interview Wednesday. “Because if you don’t have this agreement, Iran has already made clear what its direction is.”

With opposition to the agreement failing to get traction on the Democratic side, supporters may even be able to muster the 41 votes needed to block the resolution from passing in the first place, sparing Obama from having to use his veto pen. That would require eight of the 11 remaining undeclared senators to decide in favor of the deal.

“This agreement will substantially constrain the Iranian nuclear program for its duration, and compared with all realistic alternatives, it is the best option available to us at this time,” Casey said.

Republicans in Congress and running for president unanimously oppose the deal.