Senator Lindsey Graham, Republican of South Carolina, called on Thursday night for the assassination of President Vladimir V. Putin, saying in a television interview as Russian forces shelled a nuclear power plant in Ukraine that somebody in Russia should “step up to the plate” and “take this guy out.”

“Is there a Brutus in Russia?” Mr. Graham asked on Fox News. “Is there a more successful Colonel Stauffenberg in the Russian military? The only way this ends is for somebody in Russia to take this guy out.”

“The only people who can fix this are the Russian people,” Mr. Graham continued. “Easy to say, hard to do. Unless you want to live in darkness for the rest of your life, be isolated from the rest of the world in abject poverty and live in darkness, you need to step up to the plate.”

In Russia, the Kremlin’s spokesman, Dmitri S. Peskov, described Mr. Graham’s statement as an instance of a “hysterical Russophobic fit” that had captured the United States. “These days, not everyone can keep a sound mind,” Mr. Peskov said. “Unfortunately, many people go mad.”

An aide to Mr. Graham noted that he had made similar comments on the conservative network Newsmax, stating that “he was OK with a coup to remove Putin as well.”

The criminal investigation into the former president crashed amid a disagreement about the merits of bringing a case. The debate pitted a new district attorney against two veteran prosecutors who had pursued a case against Mr. Trump for years.