Republicans in the U.S. Congress will have a tough job coming up with enough votes to kill a nuclear arms deal with Iran, even with many Democrats expressing skepticism about the accord.

President Barack Obama said Tuesday he would veto any measure blocking the agreement.

Congress would need a two-thirds vote to override a veto, requiring at least 13 Senate Democrats and 44 in the House to vote against their party’s leader -- if all members voted and all Republicans backed an override.

Key Democrats expressed some concerns about the deal yet stopped short of opposing it. Democratic Senator Chuck Schumer of New York said he’ll “go through this agreement with a fine-tooth comb” and that “supporting or opposing this agreement is not a decision to be made lightly.”

One of the most skeptical was Senator Bob Menendez, a Democrat on the Senate Foreign Relations Committee, who echoed Republican concerns that the deal doesn’t dismantle Iran’s nuclear capabilities.

“Bottom line is we haven’t dismantled Iran’s nuclear infrastructure, we’ve largely preserved it,” he said. “We may have delayed it and mothballed elements of it, but they can restructure it when they choose to, especially at the end of 12 years.”

‘No Trust’

Maryland Senator Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, said “there is no trust when it comes to Iran.”

The reaction of Republicans in both chambers ranged from heavy skepticism to outright opposition. House Speaker John Boehner called the agreement “unacceptable” and said that if party members decide the deal is as bad it initially appears, “We’ll do everything we can to stop it.”

Under legislation passed in May, Congress has 60 days to review the agreement before considering a joint resolution to approve or reject the deal. That means a vote likely wouldn’t happen until September, after lawmakers’ month-long August recess that will give skeptics a chance to make their case.

The historic accord aims to curb the Islamic Republic’s nuclear program in return for ending sanctions. Full implementation will be contingent on Iran meeting its obligations to curb its nuclear program and address worries about possible military dimensions of its work.

“I will veto any legislation that prevents the successful implementation of this deal,” Obama said at the White House. “This is not the time for politics and posturing.”

Representative Alan Grayson of Florida, a Democratic member of the House Foreign Affairs Committee who is running for the Senate, said he has some qualms about the deal.

Lifting Sanctions

He said those include whether lifting economic sanctions would provide oil revenue to help Iran sponsor terrorism, whether Iran will continue its missile program, and whether “this is just a pause in Iran’s nuclear weapons program, and not an end to it.”

Representative Brad Sherman, a California Democrat on the House Foreign Affairs Committee, said Shiite Muslim Iran would spend the money that comes from sanctions relief “on graft and corruption.”

“They’re going to kill a lot of Sunnis, some of whom deserve it, many of whom do not,” and also will kill Americans and Israelis, Sherman said.

The House’s top Democrat, Nancy Pelosi of California, commended Obama and Secretary of State John Kerry for their work on the agreement, though cautioned that vigilance must be maintained.

‘All Options’

“All options remain on the table should Iran take any steps toward a nuclear weapon or deviate from the terms of this agreement,” Pelosi said.

Senate Foreign Relations Committee Chairman Bob Corker has said in recent weeks that it would be difficult to amass enough votes for a veto override.

Representative John Fleming, a Louisiana Republican who was one of 25 House members who voted against the congressional review legislation in May, said it would be difficult to get the two-thirds majority to overcome a presidential veto. A better process, he said, would have been to require two-thirds support in Congress for the deal.

‘Tough Sell’

Still, House Foreign Relations Chairman Ed Royce of California said the agreement will be a “tough sell” in Congress. Senator Tom Cotton, an Arkansas Republican, contended the agreement “will pave the way for Iran to obtain a nuclear weapon” and predicted in a statement that “Congress will kill the deal.”

Senate Majority Leader Mitch McConnell said, “The Senate must now weigh why a nuclear agreement should result in reduced pressure on the world’s leading state sponsor of terror.”

Boehner of Ohio, asked by reporters whether he had already rejected the deal without examining it, said, “I’m going to review all the facts. Based on what I know now, I’m highly skeptical.”

Corker of Tennessee said in a statement that he needs to study the deal, “but I begin from a place of deep skepticism that the deal actually meets the goal of preventing Iran from obtaining a nuclear weapon.”

Terrorism ’Sponsor’

“Iran continues to be the lead sponsor of terrorism in the world and relieving sanctions would make the Tehran regime flush with cash and could create a more dangerous threat to the United States and its allies,” Corker said.

Senator John McCain of Arizona, the Republican presidential nominee defeated by Obama in 2008, said the pact was built “on the belief that somehow the Iranian government will fundamentally change in the next several years.” That is “delusional and dangerous,” McCain said.

While McConnell, Boehner and Corker didn’t say how they think Congress will vote on the deal, some Republican presidential candidates predicted lawmakers will reject it.

Senator Lindsey Graham of South Carolina, said in an interview that the plan will give Iran “cash to feed their war machine” and predicted that lawmakers will overwhelmingly oppose it.

“This deal ensures that there will be a nuclear arms race in the Mideast” and “is going to threaten the very existence of Israel,” Graham said.

Rubio’s Stance

Another Republican candidate, Senator Marco Rubio of Florida, said Obama “has consistently negotiated from a position of weakness, giving concession after concession to a regime that has American blood on its hands.” He also said Congress will vote down the agreement.

Democrats, without endorsing the deal, said it must be looked over carefully and praised Obama for reaching the agreement.

Second-ranking House Democrat Steny Hoyer of Maryland said lawmakers need to, “work carefully through every detail.” Later Tuesday, he told reporters, “I think the American people may agree with the president on this,” though he said he had no proof of that.

Israel, which says an agreement would allow Iran to produce nuclear weapons, has been lobbying Congress against the agreement.

Josh Block, president of the Israel Project, called the agreement “a realization of the deepest fears and the most dire predictions of skeptics,” and he urged Congress to reject it.

The dispute over Iran -- and Prime Minister Benjamin Netanyahu’s March 3 address to a joint session over White House objections -- has brought the U.S.-Israel alliance to its lowest point in decades.

Obama Agreed

Corker wrote the bill that gives Congress the authority to approve or disapprove the agreement with Iran, passed in May by the Senate 98-1 and the House 400-25. Obama agreed to sign the measure after it became clear that Congress had enough votes to override a potential veto of that legislation.

The law sets Congress’s review period at 60 days, which would include lawmakers’ August recess. During this time, Obama can’t waive or reduce sanctions against Iran.

If Congress votes to disapprove the agreement, the ban on lifting sanctions would continue for another 12 days to allow time for the president to issue a veto. The period then would extend for another 10 days to let Congress consider an override.

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