BRUSSELS — Groucho Marx famously quipped that he did not want to belong to any club that would have him as a member.

President Biden had no such qualms this week.

The 46th U.S. president bounded onto the global playground like a kid at recess on the first day of school, eager to rekindle the old friendships that languished over the summer and to introduce himself to the new kids in class as well.

As Biden made his way through Cornwall, Brussels and, finally, Geneva, the enthusiasm for his return to the world stage was palpable, with him declaring, sometimes multiple times a day, that America is back.

And so is he.

“America is back,” Biden said Tuesday at the Europa building in Brussels.

“America is back on the global scene,” affirmed Charles Michel, president of the European Council. “It’s great news for allies, also great news for the world.”

The Trump years had been hard for Biden, as well as for his democracy-minded pals worldwide.

A senator of 36 years and a longtime member and later chairman of the Senate Foreign Relations Committee, Biden became omnipresent on the European security conference circuit, as well as on far-flung congressional delegation trips with fellow lawmakers. As vice president, too, he handled myriad foreign policy challenges for President Barack Obama.

For four years, Biden’s fellow transatlantic leaders had braced themselves each time President Donald Trump rolled into town, and they missed the steadier hand of previous U.S. presidents, both Democratic and Republican.

During his presidency, Trump threatened to withdraw from the NATO alliance, fought to invite Russian President Vladimir Putin back into the Group of Seven, and regularly embraced dictators and other strongmen.

And so it was with evident excitement that G-7 and NATO leaders welcomed Biden back to the club of democratic nations, aligned on issues of economic and national security.

On Friday in Cornwall, England, French President Emmanuel Macron outlined the challenges facing the global community — including the coronavirus pandemic and climate change — and stressed the need for “cooperation,” while seeming to revel in Biden’s reemergence.

“I think it’s great to have the U.S. president part of the club and very willing to cooperate,” Macron said.

Photos from the conversation show a grinning Macron, his thumbs tented, sitting next to Biden on an overlook just above the aquamarine waters of Cornwall’s craggy Carbis Bay, the U.S. president’s eyes closed and his head thrown back in an expression of sheer delight.

“The United States, I’ve said before — we’re back,” Biden declared. “The U.S. is back.”

Asked by reporters whether he had convinced allies that America is, in fact, back, Biden gestured with his sunglasses to the French president and urged, “Ask him.”

“Definitely, definitely,” Macron replied.

Earlier in the trip, addressing U.S. troops at a British air base in Suffolk, Biden implied that he had purposely scheduled a summit in Switzerland with Putin as the final stop of his trip, explaining, “And only after these meetings with our closest democratic partners to develop a common agenda and renewed purpose, I’ll travel to Geneva to sit down with a man I’ve spent time with before: President Vladimir Putin.”

The tableau he depicted had the feel of a group of friends all huddling in their treehouse, scheming and getting their slingshots ready before sending out their comrade to take on the bully.

But to a leader such as Trump, the global club to which Macron so casually referred was the problem in the first place. The Queens-born outsider was always striving for acceptance in society’s various hierarchies — real estate, business, entertainment, politics — but was often dismissed as a little too gauche.

For Trump, the club represents just another version of the Washington swamp, its members looking down on the “Make America Great Again” set with scorn and giving the United States a bad deal to boot. In a blistering statement Monday, Trump made his distaste clear.

“So much USA money has been given away to the ‘Club,’ as President Macron of France likes to call it, and to NATO, despite the fact that those countries have taken economic advantage of the United States for many years — until I came along,” Trump’s statement read. “Not fair to America, or the American taxpayer!”

But if Trump’s worldview is that everyone poses a threat, Biden looks around and sees potential friends scattered about. Not only does he want to join the club, he wants to be its leader.

To wit: Biden announced Thursday that the United States would purchase 500 million Pfizer-BioNTech coronavirus vaccine doses to donate to struggling countries, spearheading the G-7’s broader effort to provide 1 billion vaccine doses worldwide.

On Biden’s first foreign trip abroad as president, the warm sentiment and desire for belonging seemed mutual. On Thursday, British Prime Minister Boris Johnson enthused that Biden’s approach was like a “breath of fresh air.”

And on Monday, NATO Secretary General Jens Stoltenberg summarized Johnson’s description of the transatlantic security summit, saying the British leader had described the meeting to fellow leaders as “like the first day back at school, seeing all your old friends again.”

The one main area of division — on how hard to push China over human rights violations and its heavy-handed economic expansion — was largely papered over. To Biden’s satisfaction, the final communiques out of the G-7 and NATO both mentioned China.

At his first news conference abroad on Sunday, shortly before departing England for Belgium, Biden was careful to stress that the bonhomie was about the return of American democratic values generally, not him specifically.

“I noticed there was a lot of coverage of my individual comments made by my colleagues about how we were all getting along together,” he said. “But the truth of the matter is: We did. It wasn’t — I felt it wasn’t about me, but it was about America.”

Asked at a news conference here Monday whether his fellow leaders were worried that his summit with Putin on Wednesday would serve as a reward for the misbehaving Russian leader, Biden was adamant that nearly everyone was on the same team.

“There is a consensus,” Biden said. “And they thanked me for being willing to talk with them about the meeting and what I was — what I intended to do.”

And Tuesday, as Biden headed out of town to Geneva for his final summit, the Europeans were in good spirits.

Even though European Commission President Ursula von der Leyen didn’t get everything she wanted out of her Tuesday meeting with Biden — most notably, painful U.S. tariffs on European steel exports were left in place, for now — she was almost giddy after their discussion as she addressed reporters alongside Michel, her counterpart.

“The way he explained to the two of us how much he cares about Europe,” she declared. “He said, ‘We need, we Americans need Europe,’ and the same goes for us.”

Just hours earlier, Biden had greeted von der Leyen and Michel with his arms outstretched, joking, “Aren’t you tired of seeing me?”

But the club was still basking in the return of its favorite member.

“It’s a pleasure,” Von der Leyen replied.

Michael Birnbaum and Anne Gearan contributed to this report.