Biden Called Putin a ‘Crazy S.O.B.’ The Kremlin Called Biden a ‘Cowboy.’

President Biden called Vladimir V. Putin, the president of Russia, a “crazy S.O.B.” during an evening fund-raiser in California, which the Kremlin dismissed as “Hollywood cowboy-style behavior.”

“We have a crazy S.O.B. like that guy Putin, and others, and we always have to worry about nuclear conflict,” Mr. Biden told a crowd of donors in San Francisco on Wednesday night.

Mr. Biden’s comments drew the ire of Moscow, resulting in a blunt tit-for-tat.

Dmitri S. Peskov, the Kremlin spokesman, accused Mr. Biden of performing for his domestic audience.

“It is clear that Mr. Biden is demonstrating Hollywood cowboy-style behavior to serve domestic political interests,” Mr. Peskov said.

In a television interview, Mr. Putin said he thought he knew why Mr. Biden had lashed out. The Russian president had said last week that it was in Russia’s interest for Mr. Biden to win a second term — a statement seen by some as a roundabout way of saddling Mr. Biden with the endorsement of one of America’s biggest adversaries.

Mr. Putin said he believed Mr. Biden’s remark was a result of that endorsement.

“He cannot say: ‘Volodya, good boy, thank you, you helped me a lot.’ We understand what is happening with internal politics in the U.S.,” Mr. Putin said, using a nickname for Vladimir.

In California, Mr. Biden also slammed former President Donald J. Trump, for comparing his legal troubles to the death of Aleksei A. Navalny, the Russian opposition leader.

“If I stood here 10 to 15 years ago and said all this, you’d all think I should be committed,” Mr. Biden said. He added that Mr. Trump has been terrible for the Republican Party.

“A lot of Republicans I disagree with, but they’ve been decent women and men. They at least had an American moral center.