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BONN, Germany — When President Trump announced in June that the United States would withdraw from the Paris agreement, America officially ceded its global leadership on climate change.

The retreat had actually begun months earlier, when climate change disappeared from most government websites and vanished from America’s domestic and international agendas. No longer would the United States federal government address climate change at home or raise global warming with ministers and heads of state, as former President Barack Obama and his cabinet routinely did.

It was a dramatic shift, and it was meant to be.

“I was elected to represent the citizens of Pittsburgh, not Paris,” Mr. Trump said in repudiating the accord. “The Paris climate accord is simply the latest example of Washington entering into an agreement that disadvantages the United States to the exclusive benefit of other countries.”