President Vladimir V. Putin of Russia shocked the audience at the annual security conference in Munich in 2007 by demanding the rollback of domineering American influence and a new balance of power in Europe more suitable to Moscow.

He didn’t get what he wanted — then.

Nearly two decades later, during the very same conference, top officials from President Trump’s cabinet made one thing clear: Mr. Putin has found an American administration that might help him realize his dream.

Comments by Defense Secretary Pete Hegseth and Vice President JD Vance raised fears among attendees that under the new administration the U.S. might align with Russia and either assail Europe or abandon it altogether.

Such a shift, analysts say, would give Mr. Putin a previously unthinkable victory far more momentous for him than any objectives in Ukraine.

“Since the dawn of the Cold War in the late 1940s, the Kremlin has dreamed of pushing America out of its role as the cornerstone of European security,” said Andrew S. Weiss, vice president for studies at the Carnegie Endowment for International Peace. “Putin surely is savvy enough to pounce on any openings provided by the new administration.”

The presence of American troops has been the underpinning of 80 years of peace in Western Europe since the end of World War II. But in a speech in Warsaw on Friday, before his arrival at the conference, Mr. Hegseth warned European leaders they shouldn’t assume that the U.S. will be there forever.

Later in the day, at the Munich conference, Mr. Vance delivered an even scarier message for many European attendees: The enemy he sees isn’t Russia or China, but Europe itself.

Mr. Vance set about attacking European nations for using what he called undemocratic methods to restrain far-right parties that in some cases have been backed by Russia. He argued that the continent needed to recognize the desires of its voters, stop attempting to moderate disinformation in undemocratic ways and instead allow such parties to thrive as the will of the people.

“If you’re running in fear of your own voters, there is nothing America can do for you,” Mr. Vance said. “Nor, for that matter, is there anything that you can do for the American people who elected me and elected President Trump.”

Mr. Vance hit out in particular at Romania, where the country’s constitutional court in December canceled a presidential election that an ultranationalist backed by an apparent Russian influence campaign looked poised to win. The election has been rescheduled for May.

“If your democracy can be destroyed with a few hundred thousand dollars of digital advertising from a foreign country, then it wasn’t very strong to begin with,” he said.

The presence of American troops has been the underpinning of 80 years of peace in Western Europe since the end of World War II. But in a speech in Warsaw on Friday, before his arrival at the conference, Mr. Hegseth warned European leaders they shouldn’t assume that the U.S. will be there forever.

Later in the day, at the Munich conference, Mr. Vance delivered an even scarier message for many European attendees: The enemy he sees isn’t Russia or China, but Europe itself.

Mr. Vance set about attacking European nations for using what he called undemocratic methods to restrain far-right parties that in some cases have been backed by Russia. He argued that the continent needed to recognize the desires of its voters, stop attempting to moderate disinformation in undemocratic ways and instead allow such parties to thrive as the will of the people.

“If you’re running in fear of your own voters, there is nothing America can do for you,” Mr. Vance said. “Nor, for that matter, is there anything that you can do for the American people who elected me and elected President Trump.”

Mr. Vance hit out in particular at Romania, where the country’s constitutional court in December canceled a presidential election that an ultranationalist backed by an apparent Russian influence campaign looked poised to win. The election has been rescheduled for May.

“If your democracy can be destroyed with a few hundred thousand dollars of digital advertising from a foreign country, then it wasn’t very strong to begin with,” he said.

The Kremlin for years has sought to weaken Europe by boosting parties that Mr. Vance argued must be allowed to flourish. The same day as his remarks at the conference, Mr. Vance met with the leader of Germany’s extreme right movement, which is contesting national elections this month, boosting a party Russia has sought to legitimize.

Moscow has also sought to drive a wedge between the United States and Europe, realizing that a destruction of the longstanding Euro-Atlantic alliance from within will lead to a world where Moscow can wield far more power.