More broadly, Ms. Mogherini said that an administration that has made “America First” its guiding principle will find that Europe can be equally self-interested. And she politely reminded everyone just how vital Europe is to the economy and security of the United States…

She bluntly warned the administration not to nominate an ambassador to the European Union who is critical of the bloc, as has been rumored, or attempt to negotiate a bilateral trading agreement with Britain for years.

“The European Union is here to stay,” she said, adding that even though Britain may leave, “the other 27 will stick together and stay together because it’s in their interests to do so. I’ve never seen them more determined.”

Ms. Mogherini implied that the European Union could start picking off some of the United States’ most likely free-trade partners.