President Trump and French President Emmanuel Macron papered over the cracks in their relationship in a press conference Tuesday in London, but disagreed sharply over Turkey’s role in the NATO alliance.

Why it matters: Macron made waves ahead of this week’s NATO gathering by describing the alliance as unmoored and "brain dead" as a result of the U.S. pulling back and Turkey going rogue — comments Trump described Tuesday morning as “very insulting.” Trump has been agitated with Macron for weeks, Axios’ Jonathan Swan reports.

In the room: Despite his comments Tuesday morning, Trump made repeated references to his “very good” relationship with Macron.

Trump also praised what he described as NATO’s newfound strength thanks to increased spending commitments made “at my behest.”

He did, however, threaten to “deal with” countries who weren’t “stepping up,” perhaps through trade measures, and questioned at a later press conference whether it was "fair" for the U.S. to come to the defense of a "delinquent" country.

Macron emphasized that NATO is “not about numbers” and stood by his comments about the alliance experiencing “brain death.”

He said he and Trump agreed that Europe had to account for a larger proportion of the alliance’s strength and to look beyond Russia to other security challenges.

That’s when Macron raised Turkey, saying the NATO allies lacked a common definition of terrorism, given Turkey was fighting alongside “ISIS proxies” against the Kurdish YPG, “who fought with us, shoulder to shoulder, against ISIS.”

If the leaders gathered to talk about budgets but not about that situation, “we are not serious,” the French president argued.

Macron was even more forthright over Turkey’s purchase of a Russian S-400 missile system, which came despite vehement objections from NATO.

“How is it possible to be a member of the alliance, to work with others, to buy our materials and to be integrated and buy the S-400 from Russia? Technically, it is not possible,” he said.

“Second, I understand from Turkey that they want to block all the declarations of this summit if we do not agree about their definition of terrorist organizations — qualifying YPG and the others as terrorist groups, which is not our definition.”

“These two points have to be clarified if they want to be a serious member of the alliance.”

Trump, by contrast, stressed his “very good relationship” with Turkish President Recep Tayyip Erdoğan and dodged a question over whether he’d approve sanctions over the S-400 purchase — instead blaming the Obama administration for declining to sell Patriot missiles to Turkey.

Macron interjected that Turkey had the option to buy a European system but “decided not to be compliant with NATO.”

Those comments will further enrage Erdoğan, who described Macron as a novice and told him to check his own "brain death" after the French president's controversial comments.

On the question of whether France would take back foreign fighters held in Syria. Trump joked that Macron had offered “one of the greatest non-answers I’ve ever heard.”

Macron emphasized that his main concern was ISIS’ growing strength, which he attributed to destabilization on the ground. Trump contributed to that destabilization by suddenly pulling forces out, though Macron didn’t reference that decision directly.

Trump made two rather curious remarks.

Asked whether the U.S. supports the protestors in Iran — which Secretary of State Mike Pompeo and others have been actively doing — Trump said, “I don’t want to comment on that, but the answer is no.”

He later clarified that he meant that the U.S. was not supporting them financially

Trump also said the U.S. had “captured the oil” in Syria and “brought some home.”

What to watch: Both presidents emphasized the possibility of warmer relations with Russia.

“I think it’s a good thing to get along with Russia,” Trump said. “I campaigned on it. I mean, I go into big stadiums — people like it.”

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