By Patricia Zengerle
WASHINGTON (Reuters) - Supporters of the international nuclear agreement with Iran moved within one vote of mustering enough support to protect the deal in the U.S. Congress on Tuesday when two more Democratic senators said they would support the pact.
Senators Bob Casey and Chris Coons, known as Iran hard-liners, both said they backed the agreement announced on July 14 between the United States, five other world powers and Tehran.
Altogether 31 Senate Democrats and two independents who vote with them now support the deal, a potential legacy foreign policy achievement for Democratic President Barack Obama.
Backers will need 34 votes in the Senate or 146 in the House of Representatives to sustain Obama's veto if a Republican-sponsored resolution of disapproval passes both chambers.
Both Casey and Coons said they had had serious questions about the agreement, but decided it was the best option for limiting Iran's nuclear program and preferable to the United States breaking from the other countries that signed the deal.
"I was never persuaded by arguments that we could ... renegotiate successfully and get a result," Casey told Reuters in a telephone interview.
"I will support this agreement because it puts us on a known path of limiting Iran's nuclear program for the next 15 years with the full support of the international community," Coons said in a speech at the University of Delaware.
Supporters hope they will gather the 41 votes to block a disapproval resolution in the Senate and keep Obama from having to use his veto power. Congress has until Sept. 17 to pass a resolution.
Two Senate Democrats oppose the nuclear deal, along with an overwhelming majority of Republicans.
Several House Democrats announced support for the deal on Tuesday, including Adam Smith, the top Democrat on the House Armed Services Committee. More than 90 House members, all Democrats, now back the deal.
A two-thirds majority in each chamber is required to override a presidential veto and torpedo a pact in which Tehran agreed to curtail its nuclear program in exchange for relief from economic sanctions.
Some pro-Israel groups echoed Israeli Prime Minister Benjamin Netanyahu's insistence that the agreement would threaten Israel's existence by empowering Iran.
Casey said he had heard "a lot of passionate arguments" from both sides but that, despite reservations, he concluded that the agreement, with a strong deterrence policy, was the best way to keep Iran from building a bomb.