BERLIN — Chancellor Angela Merkel of Germany, Europe’s most influential leader, has concluded, after three days of trans-Atlantic meetings, that the United States of President Trump is not the reliable partner her country and the Continent have automatically depended on in the past.

Clearly disappointed with Mr. Trump’s positions on NATO, Russia, climate change and trade, Ms. Merkel said in Munich on Sunday that traditional alliances were no longer as steadfast as they once were and that Europe should pay more attention to its own interests “and really take our fate into our own hands.”

“The times in which we could rely fully on others — they are somewhat over,” Ms. Merkel added, speaking on the campaign trail after a contentious NATO summit meeting in Brussels and a Group of 7 meeting in Italy. “This is what I experienced in the last few days.”

Ms. Merkel’s strong comments were a potentially seismic shift in trans-Atlantic relations. With the United States less willing to intervene overseas, Germany is becoming an increasingly dominant power in a partnership with France.