In early 2017, American intelligence agencies delivered an unequivocal judgment about why President Vladimir V. Putin of Russia had ordered a sprawling effort to sabotage the recent American presidential election.

Mr. Putin wanted to cripple the faith Americans have in their own elections, they found, and to undermine a United States-led “liberal world order” that the Russians see as a threat to their security. As a way to achieve this goal, the assessment found, Russia worked to help Donald J. Trump win the election.

Eight years later, Mr. Trump sat in the Oval Office for a blustery meeting with President Voldymyr Zelensky of Ukraine and rendered, once again, his own judgment on that period. There was no Russian sabotage, just a “phony witch hunt” of which both he and Mr. Putin were victims.

“Let me tell you, Putin went through a hell of a lot with me,” he said.

The statement was a tell. The president sees common cause with Mr. Putin, a merging of interests forged through battles against those he believes are his and Mr. Putin’s mutual adversaries — including Democratic lawmakers, European leaders and a spectral “deep state” inside the U.S. government.

The relationship between Mr. Trump and Mr. Putin has for years been scrutinized by American government inquiries, assessments by foreign intelligence services and news media investigations. Taken together, they have unearthed evidence to support an array of theories addressing Mr. Trump’s affinity for a Russian strongman who has spent a career trying to undermine American interests.

As yet, there is no single, tidy explanation. But based solely on Mr. Trump’s public actions during his first six weeks back in office, the simple fact is that he has made few decisions on national security or foreign policy that have not been cheered by the Kremlin, making his stance toward Mr. Putin more consequential than ever.