In the months since, Washington has only toughened its stance, repeatedly criticizing Germany over its trade surplus and formally announcing that the United States would back out of the Paris climate agreement.

Combating climate change is an issue close to the chancellor’s heart, and on Thursday she saved some of her most pointed language to address her differences with the Trump administration. “Since the decision by the United States of America to quit the Paris climate accords, we are more determined than ever to make it a success,” Ms. Merkel told lawmakers.

“We will and must take on this existential challenge,” she said, “and we cannot and will not wait until every last person in the world can be convinced of climate change by scientific evidence. In other words: The climate treaty is irreversible and is not negotiable.”

Ms. Merkel said she would not pretend that differences with Washington on this stance do not exist. “It would be disingenuous if we tried to gloss over it,” she said. “At any rate, I will not do that.”

On global trade, German impatience with Washington’s stance could be seen this week, when the secretary of commerce, Wilbur Ross, canceled a trip to Berlin, where he was supposed to appear alongside of Ms. Merkel at an economic conference. Instead, Mr. Ross appeared via video link, repeating the administration’s criticism of the German trade surplus, but calling for the resumption of talks on a trans-Atlantic trade agreement. After his talk went on more than twice as long as the 10 minutes originally scheduled, organizers at the Christian Democrats’ Economic Council pulled the plug on him to allow the chancellor to take the stage.