The White House, for two months, has warmly embraced the Kremlin.

But President Vladimir V. Putin of Russia has given little in return, despite his professed willingness to cooperate.

His forces have carried on bombarding Ukraine, both on the front and deep into the Ukrainian heartland. He has barely budged in peace negotiations, freighting an agreement to a unconditional 30-day cease-fire with myriad conditions. His subordinates have dragged out talks, voicing requirements for a limited Black Sea truce in recent days.

Then, during an Arctic appearance late last week, Mr. Putin suggested a temporary Ukrainian government might need to be installed under the auspices of the United Nations and an election might need to be held to pave the way for a lasting end to the war.

The implication was that a quick peace would not be in the offing, with Mr. Putin again suggesting he couldn’t cut a deal with President Volodymyr Zelensky of Ukraine, whom Moscow for months has been tarnishing as illegitimate.

President Trump took notice.

The U.S. president told NBC News this weekend that he was “very angry” about the comments and threatened to impose tariffs on any country buying Russian oil, a measure that could dent Moscow’s most crucial source of income for the war.

“If Russia and I are unable to make a deal on stopping the bloodshed in Ukraine, and if I think it was Russia’s fault — which it might not be — but if I think it was Russia’s fault, I am going to put secondary tariffs on oil, on all oil coming out of Russia,” Mr. Trump said.