Inflation has certainly sapped support for Mr. Biden, along with the crisis at the southwestern border, fear of urban crime, anger over government spending and concerns over the president’s age as he asks voters to give him a second term keeping him in power until he is 86.

The best thing Mr. Biden has going for him politically at the moment is the likelihood that he might face Mr. Trump again next year, a rematch that his strategists assume would galvanize Democrats and independents who are not enthusiastic about the president but are inexorably opposed to the former president. Even so, according to polls, it is not a given that the president can beat his predecessor a second time, and Mr. Biden’s peers in Japan are deeply worried about a Trump return to power, remembering him as a disruptive, even dangerous, force.

This is not the first time the Group of 7 has gathered with its leaders underwater politically at home. But John J. Kirton, director of the G7 Research Group at the University of Toronto and a longtime student of the bloc, said such fallow periods typically happen when the leaders’ home countries are afflicted by severe recessions or stagflation, which is not the case now.

“At such low-in-the-polls times, the G7 summit becomes the ultimate lonely hearts club, when the leaders share their political pain, bond with one another because of it, and discuss what is working in each country to get it and perhaps them back on track,” Mr. Kirton said. “This is one way that the summit serves as the committee to re-elect the existing leaders back home.”

But Mr. Abramowitz argued that the political troubles of the G7 leaders should be taken as proof that democracy works. “Unlike authoritarian leaders, if democratic leaders don’t get the job done, they’ll be voted out,” he said. “Accountability is a strength of democracies, not a weakness.”