U.S. Secretary of State John Kerry speaks during a news...

U.S. Secretary of State John Kerry speaks during a news conference at the State Department, July 20, 2015 in Washington, D.C. Credit: GETTY IMAGES/MARK WILSON / GETTY IMAGES/MARK WILSON

WASHINGTON -- Secretary of State John Kerry Monday rejected Sen. Chuck Schumer's reason for deciding to vote against the Iran deal, arguing it is not, as the New York Democrat says, a gamble on Iran becoming a more moderate state in the future.

Kerry and Energy Secretary Ernest Moniz, on a campaign to win over members of Congress, also sought to downplay the impact of the decision by the influential Schumer, expected to be his party's next Senate leader.

"We're treating every senator equally important here. Every vote is important," Kerry said.

On Thursday, Schumer became the first Democratic senator to break with President Barack Obama on the deal, and Monday he repeated his reasoning for opposing it in an appearance in upstate Greece.

"If you believe the Iranian regime may change, then you say OK, it's a gamble," he said.

"But if you think they're going to be the same horrible regime they are now, you don't want the United States and the other nations of the world putting the stamp of approval on Iran being a threshold nuclear state," Schumer said.

Kerry, in a meeting with reporters here, said he "personally disagrees" with Schumer, saying Iran is already a threshold nuclear state.

"Look, I'm not betting," he said. "Nothing in this deal is a bet on the future of Iran's behavior. Nothing in this deal is based on trust. Everything in the deal is based on verification and a certainty that we will know what they are doing."

Kerry added the deal becomes more important if Iran's leaders continue to be a disruptive force in the region. "If you take for granted they are going to be leveraging their behavior in bad ways, you don't want them to have a weapon," he said. "If you don't have a deal, you have no inspections, you have no restraints."

The agreement among six nations led by the United States and Iran curbs its nuclear weapon development in return for lifting financial sanctions on Tehran.

In a vote next month, the Republican-controlled Congress is expected to disapprove the deal and retain the sanctions, and Obama is expected to veto that action.

Kerry and Moniz are trying to ensure they have 146 votes in the House or the 34 votes in the Senate to sustain the veto. Schumer said he'll vote no on the deal and yes to override a veto.

"He's a very savvy, capable politician," Kerry said. "I don't agree with the judgment he made. I think his calculation on the impact of this is incorrect."

But Kerry said it's his understanding that Schumer won't actively work against the deal.

In a statement, Schumer said, "This is a vote of conscience, and while I will be sharing my views with my colleagues, any attempt to twist arms or be heavy-handed on a vote of conscience backfires."

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