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.

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.

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 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. That seems to be lost with some of the things this fellow has been saying,” Mr. Biden said of Mr. Trump.

“Like he’s comparing himself to Nalvany and saying that because our country has become a communist country that he’s being persecuted like Nalvany was persecuted. I mean, where the hell did this come from?”

Mr. Trump has displayed a notable affinity for Mr. Putin over the years. He declared recently that he would “encourage” Russia “to do whatever the hell they want” to countries that he deemed to be in arrears with NATO.

Mr. Biden has been openly critical of Mr. Putin. Last week, he blamed “Putin and his thugs” for Mr. Navalny’s death. He has also called Mr. Putin a “butcher” and, after Russia’s invasion of Ukraine, he said, “For God’s sake, this man cannot remain in power.”