WASHINGTON — Hillary Clinton made it abundantly clear Wednesday night that if she defeats Donald J. Trump next month she will enter the White House with the most contentious relationship with Russia of any president in more than three decades, and with a visceral, personal animus toward Vladimir V. Putin, its leader.

“We haven’t seen a you-can’t-trust-these-guys tone like this since the days of Ronald Reagan,” said Stephen Sestanovich, who served in President Bill Clinton’s State Department and is the author of “Maximalist: America in the World from Truman to Obama.” “But even that was more a systemic criticism of the Soviet Union. This is focused on Putin himself.”

In a reversal of political roles, Mrs. Clinton, the Democratic candidate, is the one portraying Mr. Putin as America’s newest archenemy, whose underlings hack into her Brooklyn campaign headquarters, bomb Syrian civilians and threaten Ukraine and NATO allies in Europe. For a woman who presented a big red “reset” button to her Russian counterpart in March 2009 (with the word incorrectly translated into Russian), the change in tone was more striking than ever in her debate with Donald J. Trump.

She, and the Obama White House, insist they were on the right course until Mr. Putin decided he had more to gain from reviving Cold War tensions than from a quarter-century effort to integrate with the West. Now, much of the Democratic foreign policy establishment has become as hawkish as Mrs. Clinton on the subject of Russia, a view that seems almost certain to outlast the campaign.