Menendez, the New Jersey Democrat who has been leading the push to increase sanctions on Iran, said he’s taking Obama at his word that there will be no more extensions of the timeline for an agreement on dismantling Iran’s nuclear weapons program.

“It can’t be an endless string of continuations of the status quo,” Menendez said Tuesday as he left a classified briefing for the Senate Foreign Relations Committee with White House officials. “I don’t think there is any congressional appetite for endlessly continuing the status quo.”

Obama tried to set a hard deadline Monday.

“We’re at a point where they need to make a decision,” Obama told reporters. “We now know enough that the issues are no longer technical. The issues now are: does Iran have the political will and desire to get a deal done?”

Negotiators for Iran and international powers including the United States have set a deadline of the end of March for reaching the framework of an agreement, and a deadline of June for working out the details. Menendez is holding off on pushing new sanctions on Iran until the March deadline passes.

But Iran skeptics questioned how firm Obama’s deadline really is.

“I hope he means it. The question is will he actually do it? We’ll see,” said Senate Banking Committee chairman Richard Shelby (R-Ala.), who’d oversee any new sanctions legislation.

Many observers believe Obama has staked too much on completing a diplomatic opening to Iran — a country once seen as a member of the “axis of evil” — to back out of the talks now. Reaching a deal that dismantled Iran’s nukes and brought it out of its international isolation could become a key piece of his presidential legacy just as President Nixon restored diplomatic relations with communist China.

Moreover, since Iran has frozen its program as talks continue, further delays may be seen as preferable to letting Iran return to pursuing a nuclear bomb unchecked.

The problem is that many observers believe that, no matter Obama’s intentions, his options are limited if pressure doesn’t produce results.

“What will the president do if the Iranians don’t meet the March deadline?” said Ken Pollack, a former Clinton administration official and author of “Unthinkable: Iran, the Bomb, and American Strategy.” “Do we start bombing? Do we pass new sanctions? I don’t think the administration is interested in any of that stuff.”

Obama’s hard line, Pollack said, is “a statement that’s at best open to interpretation.”

Even within the White House there are mixed feelings. For instance, should there be a final deal agreement, Obama aides don’t expect the president to be part of a signing ceremony, making it a lower-key event by letting Secretary of State John Kerry do the honors. A senior White House aide said that the administration isn’t planning to take Iran at its word, referring to a Russian adage made famous by Ronald Reagan — trust but verify. This deal will have “lots of verifying, and let’s face it, probably not much trusting,” the aide said.

And within hours of Obama’s new hard line, the administration was hedging.

The end of March, State Department spokesperson Jen Psaki told reporters, “is a goal, it remains a goal. … we’ve never called it a deadline. We’ve called it a goal of when we want to achieve the political framework.”

Meanwhile, impatience is growing on the Hill.

“I trust his instincts and the negotiators’ instincts when it comes to Iran negotiations. They’ve been in a room with the Iranians. And I trust them to know when’s the right time to walk away from the table. But these negotiations can’t be endless,” said Sen. Chris Murphy, a Connecticut Democrat. “The consequences of no deal are so catastrophic that we should give it a shot, but the Iranians have had a lot of time to show good faith.”

“They have to know this is very serious, that they’re getting to the end of their timeline,” said Sen. Gary Peters, a Michigan Democrat who supports a new sanctions bill but won’t vote for it until after the March deadline passes.“The only thing the Iranians really understand is power and strength, and we’re going to show that.”

Obama may also be willing to gamble that if the talks are extended further, he could stave off sanctions by threatening to veto them, daring Congress to pass them even if they don’t have the votes to override.

“The administration has made it very clear they want this deal,” Pollack said. “And if there is the prospect of getting this deal even after March, that’s going to be their first choice.”