The New York Times | David E. Sanger: Pressed this week to define President Trump�s goals in escalating military and economic pressure on Iran, one of his top foreign policy aides ticked through a familiar list: End the country�s support for terrorism, stop its missile launches and then, most important, keep Iran more than a year away from the capability to build a nuclear weapon.

The United States would insist on �zero enrichment for Iran,� Brian H. Hook, the State Department�s special envoy for Iran, told a small group of reporters. That would assure Tehran could produce no new nuclear material, and thus never get closer to building a weapon than it is now.

It was a telling moment in a strange, circular week of mutual threats and missed signals between bitter adversaries. Designing an agreement that would assure it would take Iran a year or more to �break out� and make the fuel to build a bomb � giving the United States, Israel and others plenty of time to respond � was the driving force behind the 2015 nuclear deal that was negotiated under former President Barack Obama.

Every requirement, every concession in the deal, was measured against how it would affect that timeline. And by all accounts, that deal was working before Mr. Trump withdrew the United States from it in May 2018, calling it a �disaster.�

While Mr. Trump has insisted that he could confront Iran without leading to a military conflict, other officials in his administration have, effectively, set a red line that they said Tehran would cross at its peril.

�We are restoring deterrence while working toward a new and better deal,� Mr. Hook said. �We lost deterrence under the Iran deal.�

Officials have not specified what kind of reaction � military or otherwise � would be ordered if Iran built up enough of a stockpile of uranium and took other steps that would cross that threshold. But they have acknowledged that if President Hassan Rouhani of Iran goes ahead with plans announced last week to gradually end the limits on nuclear fuel production, it would, eventually, give Iran that capability.

Iran had shipped roughly 97 percent of its nuclear fuel out of the country, leaving only a modest stockpile, and was obeying the limits on producing more. Most experts believe it will take months before Iran has produced enough new nuclear fuel to put it within a year for having enough for a weapon. (Those estimates, however, are an inexact mix of physics, mathematical formulas and subjective judgments of the skills of Iranian scientists.)

The Trump administration�s newest declaration illustrated the confusion swirling around Congress, America�s allies and its adversaries as they press the White House about the president�s real strategic goals. Is this a confrontation about forever ending Iran�s nuclear ambitions? Ending its missile program? Stopping its support of terrorists? Or creating the conditions for the Iranian people to overthrow their clerical government?

The answers given by Secretary of State Mike Pompeo suggest all of the above, as well as the creation of an Iran that is �a normal country,� as he has put it. But, so far, Mr. Trump�s top aides have had enormous difficulty prioritizing their goals, or explaining how they turn a confrontation into a negotiation.

That may be the result of a president who knew what he didn�t like � a deal negotiated under Mr. Obama, in which key restrictions on nuclear fuel production expire starting in 2030 � before determining how he wanted to replace it.

�They were so committed to leaving the deal, because it had been negotiated by the Obama administration, that they did it without thinking through the predictable consequences,� said Vipin Narang, an associate professor at the Massachusetts Institute of Technology, who tracks nuclear proliferation issues.

�The old agreement had flaws � many of them,� Mr. Narang said. �But by ripping it up, they opened up a Pandora�s box,� because so many in Iran also had chafed at the deal because of the nuclear production it gave away.

Now Mr. Trump is confronted with the consequences of his decision. His declarations on Wednesday and Thursday that he did not want war with Iran were intended to calm the waters, and show that, no matter what his most hawkish advisers recommend, he is not steaming toward some inevitable conflict.

It also sent a mixed signal to Tehran about what the consequences would be if the clerical government resumed producing nuclear material. �He gave up his biggest piece of leverage,� said Mr. Narang, referring to the Trump administration�s vague threat that if Iran got too close to a bomb, military action by the United States or Israel could follow.

For Mr. Trump, this is a familiar pattern. He threatened North Korea with �fire and fury� in 2017, when it was testing missiles and nuclear devices. But as soon as he met Kim Jong-un, the North Korean dictator, Mr. Trump declared that the nuclear threat was over.

That was nearly a year ago, and Mr. Kim since has never ceased producing nuclear material, and likely nuclear weapons, according to American intelligence reports.

No doubt the Iranians noticed.

It is possible that Mr. Trump is just staging a confrontation to force Iran to negotiate a new deal. This week, he said he wanted to talk to Mr. Rouhani. But the initial reaction from Iran was underwhelming.

�They want to have the stick in their hands, trying to intimidate Iran at the same time calling for a dialogue,� Majid Takht-e Ravanchi, Iran�s ambassador to the United Nations, told CBS on Friday. �What type of dialogue is this?�

Rewriting the nuclear deal would bear some resemblance to what Mr. Trump did when he tossed aside the North American Free Trade Agreement, only to emerge with a new one, negotiated with Canada and Mexico, that bears a considerable resemblance to its predecessor. On that issue, Mr. Trump was in his comfort zone: Rebalancing the scales in trade in goods is what animates him most.

But nuclear strategy operates by different rules. As Mr. Trump has learned with North Korea, even the prospect of building glistening hotels on pristine beaches is not enough to make authoritarian leaders give up the technology that can keep them from being overthrown by outside powers.

Iran is not about auto parts and electronics supply chains, and getting it wrong could easily touch off a nuclear arms race in the Middle East, as Saudi Arabia openly threatens to match whatever Iran does.

That, of course, was the central dilemma facing the Obama administration making its first, secret approach to Iran six years ago. At first, Mr. Obama�s aides insisted Iran would have to give up everything, but that the Tehran government could produce no material that might ultimately be diverted to a bomb.

Eventually, American negotiators concluded after years of running into walls that it would be better to leave Iran with a face-saving token capability for 15 years, and vigorous international inspections, than walk away with no agreement and the real prospect of war.

Many of Mr. Obama�s critics, including some Democrats, have said the negotiators gave up too much. During the 2016 presidential campaign, Mr. Trump quickly homed in on the nuclear agreement�s most glaring weakness: After 15 years, the Iranians could resume unlimited fuel production.

Mr. Obama�s essential bet was that in 15 years Iran will have different leadership, perhaps more interested in integrating with the world than keeping a bomb-making capability. So he brought into the negotiation a nuclear scientist in his cabinet, Energy Secretary Ernest Moniz.

Mr. Moniz, the former head of the M.I.T. nuclear physics lab, sat for months with his Iranian counterpart, who had done his graduate studies at M.I.T. They bonded, and emerged with an agreement that Energy Department scientists certified would assure Iran would need a year or more to �break out� and manufacture the fuel needed for a nuclear weapon � until the 15-year clock ran out.

Now Mr. Trump�s negotiators have decided they need the same thing � but it must be permanent.

The schedule that Mr. Rouhani announced to his nation last week would put Iran back on the path of nuclear fuel production. Sooner or later, it would cross that one-year threshold. Iran has never enriched at the level of purity needed to produce a weapon, inspectors say, but they have come close.

�If you want to keep Iran more than a year away from the capability to build a bomb, the way to do it is to go back into the deal,� said Jake Sullivan, a former Obama administration national security official who helped open the negotiations with Tehran. �Because that�s exactly what the deal does.�

In fact, Iran�s foreign minister, Mohammad Javad Zarif, has insisted that returning to the deal is the prerequisite for discussing changes.

Mr. Trump says no way. And on Friday, he tried to turn mixed messages into a blessing. �With all the Fake and Made Up News out there,� he tweeted, �Iran can have no idea what is actually going on!�