MUNICH — European leaders have long been alarmed that President Trump’s words and Twitter messages could undo a trans-Atlantic alliance that had grown stronger over seven decades. They had clung to the hope that those ties would bear up under the strain.

But in the last few days of a prestigious annual security conference in Munich, the rift between Europe and the Trump administration became open, angry and concrete, diplomats and analysts say.

A senior German official, who asked not to be identified because he was not authorized to speak on such matters, shrugged his shoulders and said: “No one any longer believes that Trump cares about the views or interests of the allies. It’s broken.”

The most immediate danger, diplomats and intelligence officials warned, is that the trans-Atlantic fissures now risk being exploited by Russia and China.