Nic Robertson is CNN's international diplomatic editor. The opinions in this article belong to the author.

(CNN) The problem with being at the top is that everyone wants to knock you down.

America has for decades been the poster boy for all that is good and all that is possible. It is the shining city on a hill

The leader of the world's greatest superpower, it seems, no longer sets the course on world affairs.

This may all be part of Trump's "America First" policy. It may turn out fine: Ultimately the world could still bend to his will. But if the G20 was a test, some recalibration may be required -- urgently.

After Trump's meeting with Russian President Vladimir Putin last week, the only other American diplomat in the room, Secretary of State Rex Tillerson, conceded that Trump recognized the Russian position on North Korea had different "tactics and pace" to his own. "I would say the Russians see it a little differently than we do, so we are going to continue those discussions and ask them to do more."

Eschewing allies -- and in the case of the Putin meeting even eschewing his own skilled Russia experts -- minimized Trump's ability to maneuver. And at this level of international diplomacy, the pitfalls are massive -- especially when dealing with a man accused of meddling in your elections.

JUST WATCHED Putin: I think Trump agreed Russia didn't meddle Replay More Videos ... MUST WATCH Putin: I think Trump agreed Russia didn't meddle 01:13

The next day when meeting with Chinese President Xi Jinping, Trump ran in to another impasse. Back in April when hosting the Chinese leader at his Mar-a-Lago resort in Florida, he said the two countries have made "tremendous progress" and have an "outstanding relationship."

In Germany, the President's tone was less optimistic: "As far as North Korea is concerned, we will have, eventually, success. It may take longer than I'd like."

The harsh reality is that America -- despite Trump's varied Twitter proclamations to the contrary -- is being shoved aside.

None of this damage is necessarily irreparable, but it must also be worth considering at this point what can be done to shore up the US position as global guardian of much that is good.

In Paris, the French leader had a unique opportunity to explain how America's allies are seeing the Trump administration.

Macron, it seems, believes he can influence Trump and guide him back to center stage.

At a press conference Thursday in Paris, Macron said the two leaders had discussed counterterrorism and security. But the meeting was in essence about the allies getting to know each other as much as it was about setting out substantive relations.

Macron, France's youngest President, and Trump, America's oldest, make an unlikely couple. If their handshake wars don't adequately reveal the tone of their relationship, then Trump's rejection of the Paris climate accord -- which was embraced by every other nation at the G20 -- has highlighted their significant differences.

"Make our planet great again," Macron tweeted shortly afterward . This is a meeting of egos, ambitions and controlling the media narrative.

At Bastille Day celebrations, Macron got to position the French military and its potent symbolism of strength right under Trump's nose.

Meanwhile, Trump gets to grandstand and recall the two countries' shared history: It's been 100 years since US troops came to France's aid in World War I. And when, during Thursday's joint press conference, he invoked last year's Nice attack , he was able to restate his message of Western values being under threat -- a message we heard in Poland only last week.

JUST WATCHED President Trump's entire Paris remarks Replay More Videos ... MUST WATCH President Trump's entire Paris remarks 27:54

But if Trump is able to contain himself, the prize could be huge. Macron, a rising star in European and global politics, is fresh from electoral triumph and has political capital to spend.

Trump knows that for all his talk of a fast trade deal with the UK, the European Union -- at least in the short term -- remains a juicer opportunity for the United States and might help Trump create some of those jobs he keeps talking about.

At a stroke, he can acquire the new poster boy of Western liberalism as an ally, make progress on an important trade deal for the country and, most importantly, show European allies that though America may look different, it's still at the table.

As ever with Trump, it won't be until after the visit that we learn how intently he has listened to Macron or how likely he is to take anything he has said on board.

Both leaders already know only too well where their differences lie. But their short time together will give them a chance to sense where cooperation might become possible.

Macron has called for another climate change conference for Paris in December, following on from the famous accord summit two years ago. Trump hinted he might now be ready to reconsider his isolationist anti-agreement position.

If Trump can escape his Washington trench warfare -- be it the encirclement of Russia's election meddling or the pressure to deliver on health care -- he may find in Macron a leader willing to engage where he can. As we heard Thursday, Syria and counterterrorism are good areas for Trump.

Both presidents agree that Syria's Bashar al-Assad can stay for now. Both view ISIS as a threat to national -- and international -- security.

An agreement between the two without further pitfalls could paper over some of the gaps that Trump is opening up between himself and America's traditional European partners. Agreement with Macron, a would-be modern-day Bismarck , would likely burnish Trump's not insubstantial sense of self and buy him some much needed international credibility.

Trump's visit to Paris will likely leave the young political star feeling that his valuable political capital, for now at least, has been wisely invested. Even he, the darling of the modern European dream, is like Trump beset by his own modest hubris. The difference is that Trump's, unlike Macron's, has a diminishing orbit.