Washington (CNN) Hours of intensive talks and elaborate displays of bonhomie between President Donald Trump and his French counterpart Emmanuel Macron on Tuesday failed to yield clarity on the fate of the Iran nuclear deal, which Trump has derided and Macron hopes to salvage.

More successful were Macron's appeals to rethink an immediate exit of US troops from Syria, which Trump conceded could not happen until the US is able to "leave a strong and lasting footprint."

It amounted to a split outcome for Macron, who arrived in Washington hoping to sway Trump away from isolationist decisions that loom in the coming months. Trump has insisted his pledges to rip up the Iran deal and bring American troops home from war amount to promises his voters expect him to fulfill.

Trump opened the day railing against the Iran accord, calling the Obama-era agreement "insane" and "ridiculous" for failing to contain Tehran.

Later, during a news conference, he sounded a more conciliatory note and maintained he could soon strike an agreement with his visitor, who laid out his own vision for pact.

"We can be flexible. You know, in life you have to be flexible, and as leaders of countries, you have to show flexibility," Trump said.

But Trump declined to say whether he would sign on to a Europe-brokered supplemental agreement to the Iran deal. And he offered an ominous threat to Tehran should it resume its nuclear program.

"They will have bigger problems than they ever had before," he said.

The lingering dispute over the Iran deal proved that neither dinners of Dover sole nor a glitzy military welcome could paper over the two leaders' differences during an elaborate state visit, the first of Trump's presidency.

Earlier in the day, the two men put forward an elaborate show of friendship on the South Lawn, reviewing cordons of troops in formation and recalling the long history between the US and France. They are due to sit for Trump's inaugural state dinner on Tuesday evening, with rack of lamb and jambalaya on the menu.

Throughout the day, the two leaders sought to play up in their body language the image of a global "bromance." But the persistent back-patting, handshaking and pecks on the cheek came ultimately to assume a competitive undertone, with the germ-averse Trump standing rigidly as Macron grasped his forearm and Trump happily flicking what he said was a flake of dandruff from Macron's navy suit.

Macron acknowledged during his remarks Tuesday that he was visiting a strong-willed peer.

"It's not a mystery, we did not have the same starting positions, and neither you nor I have a habit of changing our stances or going with the wind," the French President said through a translator. "That being said, I can say that we've had a very frank discussions, just the two of us."

Little clarity on Iran

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Trump has threatened to pull out of the Iran deal and snap back US sanctions on Iran by May 12 unless major changes are made to the agreement brokered by the previous US administration, which capped Iran's nuclear program in exchange for relief from economic sanctions.

Trump on Tuesday decried the deal as failing to address Iran's ballistic missile program or its support of terror groups in the Middle East.

France, Germany and the United Kingdom -- key signatories to the deal -- are in the midst of negotiations with the US aimed at assuaging some of Trump's concerns, but large gaps still remain.

Macron said on Tuesday he was open to a new agreement that would address Trump's concerns while not tearing apart the existing deal. But Trump offered no indication of which direction he may go.

"Nobody knows what I'm going to do on the 12th," Trump said, referring to the deadline. "This is a deal with decayed foundations. It's a bad deal, it's a bad structure, it's falling down. It should have never, ever been made."

Already, some US administration officials have been preparing options for withdrawal from the agreement, hoping to be ready should Trump abruptly make his announcement over Twitter. Macron's visit was viewed as critical to swaying Trump toward a compromise, rather than the all-or-nothing approach he has signaled on the Iran deal.

Trump offered scant assurances to Macron that he was reconsidering his pledge to exit the Iran agreement. But he did signal a compromise may be near.

"We could have at least an agreement among ourselves fairly quickly," he said during talks in the Cabinet Room. "I think we're fairly close to understanding each other. And I think our meeting, our one-on-one went very, very well."

And he signaled he was willing to reconsider his demand that US troops exit Syria soon, indicating he didn't want other countries like Iran and Russia to gain a foothold.

"I do want to come home, but I want to come home also having accomplished what we have to accomplish," he said.

Elaborate welcome

Trump is deploying the full trappings of formal state entertaining for the first time in the hopes an elaborate display of diplomacy can lead to a deeper bond with the young French leader. First lady Melania Trump, who emerged from the South Portico on Tuesday wearing a dramatic wide-brimmed white hat , has been overseeing preparations, including the three-course state dinner on Tuesday.

Standing before a military display on the South Lawn, Trump hailed the US-France alliance without mentioning the areas of difference. Macron, he said later, was doing a "great job" as President.

Macron, however, did not avoid the topic, saying the differences over climate change were surmountable.

"On this issue, we do not always agree as to the solutions, but in the end, such is the case in any family and in any friendship, and it is also where the fate of our children is at stake," he said through a translator.

He also warned against the rise of "aggressive nationalisms that deny our history and divide the world," a potent subject both in France, where anti-Semitism and nativist immigration stances have swelled, and the United States, where white nationalist rallies have drawn condemnation, though not from Trump.

"It is together that we will build a new strong multilateralism that defends pluralism and democracy in the face of ill winds," Macron said.

Underlying competitiveness

The French leader -- who has been dubbed a "Trump whisperer" by some -- has forged one of the closest relationships Trump maintains with any world leader, some of whom he has openly feuded with or belittled.

But beneath the outward bonhomie is an underlying competitiveness, according to US and French officials familiar with the two men's relationship. Both are alpha males highly attuned to their own reputations, and each entered office with grand promises of shattering their country's political status quo. Officials in both countries have downplayed the notion of a "bromance," insisting the two men are not close personal friends but rather closely aligned allies.

Ever since May, when the two men met for the first time inside the US ambassador's residence in Brussels, fascination has swirled around their relationship. That first meeting was marked by strained grins and a lengthy, white-knuckled handshake that immediately went viral online.

Even before that session, which occurred on the sidelines of a NATO summit, Macron has carefully approached his interactions with an unpredictable American leader. He studied videos of Trump's handshakes, which sometimes include a firm tug inward. He and his aides continue to closely monitor Trump's Twitter feed for a daily reading of the US President's mood and his shifting policy sentiments.

On Tuesday, the physical assertiveness continued. Macron seemed intent on kissing Trump on both cheeks, in the French style, upon every greeting. During their joint news conference, he reached over on occasion to grab Trump's arm as he punctuated his point.

Trump, meanwhile, decided a photo opportunity on the Oval Office was the ideal moment to highlight Macron's scalp care.

"I'll get that little piece of dandruff off," Trump said, brushing an invisible piece of dust from Macron's shoulder.

"We have to make him perfect," he said. "He is perfect."