The lone Democratic senator to publicly oppose President Barack Obama's nuclear agreement with Iran said Tuesday that even if the U.S. backs away and other countries lift their sanctions, Iran still will feel "meaningful pressure" from the U.S. penalties.

The deal between would curb Iran's nuclear program in exchange for billions of dollars in relief from crippling sanctions.

New York Sen. Chuck Schumer's view sharply contrasts with European leaders who have told U.S. lawmakers that if Congress were to reject the deal, the international sanctions would unravel, undermining global pressure on Iran.

Schumer also said that sanctions aimed at companies that do business with Iran could force U.S. allies and trade partners back to the negotiating table.

"Let's not forget, those secondary sanctions are very powerful," Schumer told reporters in New York as he detailed a decision he first announced last week.

He said these sanctions alert corporations, such as the French oil company Total, that if it deals with Iran, it cannot deal with the United States.

"We have that powerful tool, and if used, I think that's a better, better chance in a very difficult world than an agreement that is so totally flawed," Schumer said.

Schumer's opposition was seen as a blow to the Obama administration. White House lobbying on Capitol Hill had produced a steady stream of support from Democrats.

Schumer is a leading congressional ally of Israel, a major fundraiser and savvy strategist for his party, and represents a state that is home to more than a million-and-a-half Jews. He is in line to lead Senate Democrats after the 2016 elections.

He was asked by reporters whether he intended to lobby colleagues to vote with him.

"Certainly, I'm going to try to persuade my colleagues that my viewpoint is right, but anyone who thinks you can force somebody to vote with you in the Senate doesn't understand the Senate," he said. "This is a vote of conscience. It was a vote of conscience for me. It will be a vote of conscience for my colleagues."

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Caruso reported from New York.

Chuck Schumer, the only Democratic senator who's come out so far against President Barack Obama's nuclear agreement with Iran, is detailing his opposition.

The New York lawmaker says even if the U.S. walks away from the deal and other countries end their sanctions, the penalties still imposed by the United States will exert "meaningful pressure" on Iran.

The deal reached last month would curb Iran's nuclear program in exchange for billions of dollars in relief from the economic sanctions.

Schumer's view sharply contrasts with European leaders who have told U.S. lawmakers that if Congress rejects the deal, the international sanctions will unravel.

Schumer's decision was a blow to the Obama administration after White House lobbying had produced a steady stream of support from Democrats.