(Bloomberg Opinion) — Although Group of Seven summits rarely produce much of value, they can generally be relied on to avoid making things worse. This weekend’s gathering in Biarritz, France, was a notable exception.

With concerns about the global economy mounting, and security and environmental challenges demanding fresh purpose and clarity from the U.S. and its allies, the summit only compounded the risks.

There’s no mystery about who to blame: an American president who has made chaos his method of government and renounced the global leadership role that all his modern predecessors, much to the U.S.’s benefit, were eager to discharge.

Disarray was the summit’s only constant. First, in off-the-cuff remarks to reporters, President Donald Trump suggested that he was having second thoughts about the policy that he’s proud to call a “trade war.”

Clarification followed: An official explained that the president was only wondering whether it might have been better to make tariffs against China even higher. Then, on Monday, Trump said China had called U.S. trade officials asking to restart the talks; Beijing seemed puzzled by the news.

“I think [the other governments] respect the trade war,” the president had remarked Sunday. How could they not?

Earlier Trump had “hereby ordered” (in a tweet, of course) “our great American companies … to immediately start looking for an alternative to China, including bringing your companies HOME and making your products in the USA.”

Because the president lacks the authority to hereby order any such thing, another clarification was required. The president said he could declare a national emergency and this would provide all the powers he would need — you know, should he abruptly choose to decouple the world’s two largest economies and thereby engineer a global slump.

Turning to other business, the U.S. president missed few chances to contradict either himself or his summit partners. Should Russia be readmitted to these meetings, for instance? France, Germany and the U.K. are wary; Trump says he likes the idea. Japanese Prime Minister Shinzo Abe deplored North Korea’s latest missile tests, saying they violated United Nations Security Council resolutions. President Trump said, “We’re in the world of missiles, folks, whether you like it or not.”

Perhaps finding inspiration in the U.S. example, French President Emmanuel Macron added a little Trump-like disarray of his own, springing a visit to Biarritz by Iranian Foreign Minister Javad Zarif on the rest of the group. (Zarif met with Macron but not the other leaders.) French officials said the G-7 had asked the French president to pursue the possibility of dialogue with Iran. The U.S. demurred, but “I can’t stop people from talking,” Trump said.

Indeed you can’t. That’s the problem with grandstanding and fomenting confusion. Such antics are apt to catch on.

Global economic momentum is fading, not least due to Trump’s fondness for trade wars — and bear in mind that if a new recession is the result, central banks will lack the means to respond effectively. Global measures to combat climate change remain woefully insufficient. Global safety and security have been compromised by the rapid decay in conventions and institutions of international cooperation.

What’s truly remarkable is that all of these challenges are the result of deliberate acts of U.S. policy. The summit couldn’t have put everything back together — that’s the work of years, starting with a different U.S. president — but it could have offered some respite. Instead, the planet’s most powerful politician has dug the world into an even deeper hole.

–Editors: Clive Crook, Nisid Hajari