Screens on Kindle readers will crack paging through books explaining what Mr. Obama could have, should have and would have done. For now, the short version is enough: America and the world failed because they didn’t do what Barack Obama told them to do. For seven years, he has been instructing everyone on the “right thing to do.” If Mr. Obama seems down these days, it is because so many—from John Boehner to Vladimir Putin to the man in the street—persisted in doing the wrong thing.

Iran’s ayatollahs got the Obama message, though, and that deal is the legacy.

The other half of the non-domestic legacy is supposed to be climate change. His appearance in Paris this week was Mr. Obama’s last turn on the big global stage, barring a national crisis. Anyone watching the angular figure of the American president making nonstop pleas at the Paris climate summit this week had to be struck by a sense of what the French would call tristesse, a melancholy, even pathetic sadness.

He alone in Paris seemed to take seriously the notion that the climate windmills can be reset to less than 2 degrees Celsius above “preindustrial levels.” In the last of many public apologies for the U.S., Mr. Obama confessed that his own nation is a grievous “emitter.”