The White House’s campaign to keep Congress from messing with its carefully constructed talks with Iran over its nuclear program have stepped into overdrive after support for a new round of sanctions threatens to reach veto-proof majorities.

On Monday, Press Secretary Jay Carney repeatedly advised Congress against acting now — one day after President Barack Obama declared he would veto a sanctions bill while announcing the latest agreement with Iran on interim steps to limit its nuclear program. Carney had earlier said that Obama would veto the sanctions bill, but that hasn’t stopped backers from pushing forward.

Carney called legislation unnecessary because Congress could act very quickly to impose new sanctions if talks fall apart.

“We’re very confident Tehran understands that failure to abide by its commitments in the implementation agreement or failure to reach comprehensive resolution would result in action by the United States and by the international community,” Carney said.

The Iran sanctions push pits several members of top Democratic leadership — notably Sen. Charles E. Schumer of New York, the No. 3 Democrat, and Foreign Relations Chairman Robert Menendez of New Jersey — against the president, creating a particularly tense and unusual situation for Obama. The White House is more accustomed to knocking down House opposition while relying on a friendly Senate as its backstop.

So far, the bill, which would impose new sanctions against Iran if it does not reach a comprehensive nuclear deal, remains effectively in Senate Majority Leader Harry Reid’s legislative closet, and aides suggest the Nevada Democrat will keep it there for now.

“There is not a big clamor for a vote” at the moment, said a senior Democratic aide, who noted that while many senators have voiced support for the bill, not all of them are all demanding immediate action.

Another senior aide predicted last week that the bill wouldn’t come up anytime soon and denied a CNN report that it could come up the week of the president’s State of the Union address.

Reid at one point last year said the Senate would address the issue, only to apparently change his mind and move to other matters instead. The House already passed additional Iran sanctions last year, leaving the Senate as the president’s backstop.

The administration is desperate to keep it that way, repeatedly warning of disaster if Congress interferes with the delicate talks.

“Why would you put all of that progress at risk to pass a sanctions bill that the administration is not asking for and that risks dividing the international community?” a senior administration official asked reporters over the weekend as the administration announced the latest agreement. “Because in fact, not only do we think that a new sanctions bill could derail these talks. Ultimately, a new sanctions bill could undermine the sanctions regime that we have built so meticulously over the course of the last several years, because, essentially, if the talks are derailed by new U.S. unilateral sanctions, Iran would take that case to the international community and seek to create divisions in the international community.”

In addition to the fear of a broader diplomatic disaster, a congressional smack down of Obama on foreign policy — an area where presidents usually have primary authority — would damage the institution more generally and hurt his ability to negotiate any number of other international deals.

Then there is the other fear in the White House — that the collapse of talks could lead to a costly war.

“Frankly, this is our opportunity to achieve a peaceful resolution to this issue,” the senior official warned. “And because of that opportunity, Congress should not take action that closes the door on diplomacy.”

But doubts remain within Congress about Iran, some of our international partners and even the administration’s own eagerness to cut a deal.

And some on Capitol Hill believe that congressional saber-rattling will give Obama leverage in the talks — even if the new proposals never come to a vote.

But the administration official dismissed the idea that actually voting on more sanctions would help.

“Nobody doubts that Congress could move in a nanosecond to impose additional sanctions if Iran doesn’t comply with the agreement or if we aren’t able to negotiate an agreement during the course of negotiation. So the leverage is already there,” the official said.

Carney declined, when asked by a reporter Monday, to characterize the talks as a “good cop, bad cop” situation with Congress helpfully playing “bad cop.”

Humberto Sanchez contributed to this report.