On Sunday's “Face the Nation,” Kim Darroch offered fans of the Iran deal a reason to hope.

The British ambassador to the United States told host Margaret Brennan that he believes the 2015 accord will be saved.

President Trump is famously opposed to the agreement, which offered Iran relief from major economic sanctions in exchange for curbs on its nuclear program. Trump has called it the worst deal in U.S. history, once suggesting it was so bad that “there has to be something else going on.”

“Who would make that deal?” he asked in 2016.

Candidate Trump told voters he would pull out of the agreement. As president, he has been slightly more measured. Last October, he officially disavowed the deal, although he stopped short of terminating it. Instead, he passed the buck to Congress, giving it the power to reimpose sanctions — or not.

Now, however, he is considering whether to restore U.S. sanctions against Iran. If that happens, it would put all of the treaty's signatories in a tricky position. A complete collapse of the agreement would also make it harder to keep Iran from developing nuclear weapons, if it chose to do so.

By all accounts, Iran has complied with the deal. But Trump says the deal is far too weak to really constrain the country's nuclear ambitions. Among his concerns: The regulations on Iran expire at a certain point. These “sunset clauses” lift restrictions on some Iranian nuclear activities after 10 to 15 years. The treaty does not prohibit the testing of ballistic missiles, which Iran has continued to do. The Trump administration has also criticized Iran for its support of militant groups such as Hezbollah and Hamas, arguing that the country is destabilizing the region.

On Sunday, Darroch said that Britain has some ideas for addressing Trump's concerns. “We think that we can find some language, produce some action that meets the president’s concerns,” he said, noting that his team was working closely with France and Germany, other advocates of the deal.

Darroch also told Brennan that Trump and British Prime Minister Theresa May spoke Saturday, and that Trump told May “a final decision hasn't yet been taken.” Darroch said he would personally lobby national security adviser John Bolton, as well.

It is unclear what those fixes would look like. In the past, European negotiators have said there are opportunities to tweak the deal so that missile tests are limited and banned. They are also open to pushing Iran to agree to give inspectors unfettered access to Iranian military bases. It's unclear whether Iran would agree to those terms.

“We think it's a good deal,” Darroch said. “We have been talking at senior official level to the administration with our French and German colleagues for several weeks now. We think we're making progress. We haven't got there yet. We have a few days left to see if we can find a way through.”

Darroch's interview came just days before British Foreign Secretary Boris Johnson flies to Washington for two days of talks with officials. His aim is to salvage the accord ahead of Trump's deadline Saturday. Last month, French President Emmanuel Macron made an impassioned case to Trump and in a speech to a joint meeting of Congress against scrapping the deal.

But on the last day of his visit, Macron told reporters that he did not think he had succeeded.

“My view is … that he will get rid of this deal on his own, for domestic reasons,” Macron said at the end of a three-day visit, according to the BBC.

Correction: An earlier version of this story misrepresented national security adviser John Bolton's position on the Iran deal.