President Trump speaks to the media from the South Lawn of the White House on Friday as he departs for the G-7 Summit in Canada. (Jabin Botsford/The Washington Post)

As President Trump departed Washington on Friday to head to Quebec for an annual summit with the heads of the Group of Seven leading economies, the U.S. leader suggested that the summit needed another attendee: Russia's Vladimir Putin.

“Now, I love our country. I have been Russia’s worst nightmare … but with that being said, Russia should be in this meeting,” Trump told reporters at the White House. “It may not be politically correct, but we have a world to run. … They should let Russia back in.”

The comments drew ire from Trump's critics, who felt not only that the U.S. president has been unusually soft on Russia during his term but also that election interference ordered by Putin is the reason Trump is in the White House.

The U.S. president did not mention that Russia had been ejected from the G-7 — then dubbed the G-8 in reflection of its larger membership — as a response to Moscow's annexation of Crimea in 2014.

But with the comment about Russia, as well as hostile remarks about traditional G-7 allies such as France, Canada and Britain, Trump has hit at potentially weak foundations of the distinctly informal G-7 grouping. Its membership has grown and shrank over the past four decades, reflecting an ad hoc nature that was once the grouping's greatest strength — but could still become its biggest weakness.

A Cold War concept at heart, the idea that there was a need for a forum for the world's leading democracies first gathered steam in the early 1970s. One of the first meetings of this kind took place in the library of the Nixon White House in 1973, where U.S. Secretary of the Treasury George Shultz convened the finance ministers of Britain, France and West Germany. Later, when Japan joined this grouping, it became known as the “Group of Five.”

In 1975, the first “Group of Six” meeting took place — with Italy as the newest addition. With annual meetings, the group would continue to grow: Since 1981, the European Union has also participated as a “nonenumerated” member. And when the Cold War ended, there was room for further expansion. Russia, now officially a democracy, joined in 1998 after a few years of partial participation, making it a “Group of Eight.”

The expansion of the group was made possible by two factors. First, there were no real criteria for entry: The only restrictions on membership were that a country should be a democracy with a developed economy. Secondly, it was not a formal institution with a charter that dictated how it should operate; in fact, the grouping was designed as a reaction against the formality of something such as the United Nations.

The agenda was set instead by a presidency that rotated among the members. President Bill Clinton was heading the G-7 presidency in 1997 when the U.S. leader argued that inviting Russia into the group would push Moscow toward taking a constructive role with its neighbors and worry less about NATO expansion in Eastern Europe. While many in the group had objected, former deputy secretary of state Strobe Talbott later recalled that Clinton had told him it was a simple deal.

“We get ’em into the G-7 and they get out of the Baltics. If they’re part of the big boys’ club, they’ve got less reason to beat up on the little guys,” Talbott wrote in his memoir.

This deal worked in the short term: Clinton was able to lean on Russia's Mikhail Gorbachev during the Kosovo war, using Russian influence on Serbia to help end the crisis. But after Putin took over the Kremlin, Russia was increasingly at odds with its G-8 partners. Even after it was kicked out, Russia has neither relinquished Crimea nor apologized for its actions in Ukraine. Many blatantly aggressive moves, including the attempt to influence the 2016 U.S. election, took place after Moscow had its G-7 membership rescinded.

Critics of Trump's idea to bring Russia back into the group could point out that, as loose as the requirements for membership are, Russia may not meet them. Putin has been in power in one form or another for almost two decades, and few observers think that Russian elections are free and fair. And while the Soviet Union was once a major economic powerhouse, modern Russia's finances are more shaky: The World Bank ranks its economy as the 12th-largest in the world, marginally ahead of Spain or Australia.

However, these arguments could well have been made in 1997, too — Boris Yeltsin's Russia was an economic disaster and a fledgling democracy at best. And talking about economics raises bigger questions about G-7 membership, too.

At its peak in the 1980s, the aggregate GDP of the group was almost 70 percent of the global economy, but it has dropped to below 50 percent, according to statistics compiled by the Council on Foreign Relations. Some of the world's most economically powerful democracies are not included in the current lineup: India, Brazil and South Korea, to name three. These countries, as well as the clearly nondemocratic behemoth China, make up part of the larger and perhaps more relevant G-20.

Worse still, the G-7 is not politically aligned. Over the past few days, Trump — a leader who favors unilateralism over multilateralism — has engaged in a war of words over trade and other issues with Canada's Justin Trudeau and France's Emmanuel Macron. The French leader, in particular, has raised the prospect of isolating the United States within the grouping — or perhaps even shrinking the Group of Seven once more into a Group of Six.

“Maybe it doesn’t bother the American president to be isolated, but it doesn’t bother us to be six if need be,” Macron said Thursday.

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