"Is there a Brutus in Russia? Is there a more successful Colonel Stauffenberg in the Russian military?" Graham tweeted, referencing the Roman politician who participated in the assassination of Julius Caesar and the German military officer who attempted to kill Adolf Hitler.

"The only way this ends is for somebody in Russia to take this guy out," he said. "You would be doing your country - and the world - a great service."

Graham added that if Russians do not want to live in darkness and be isolated from the rest of the world, then "you need to step up to the plate."

Other members of Congress swiftly criticized Graham's tweets as reckless, including members of his own party.

Republican Sen. Ted Cruz of Texas said, "This is an exceptionally bad idea." Sanctions and boycotts of Russian oil and gas are solutions, along with military aid for the Ukrainians, Cruz said.

"But we should not be calling for the assassination of heads of state," he added.

Rep. Marjorie Taylor Greene, R-Ga., called Graham's remarks "dangerous" and "unhinged."

"We need leaders with calm minds & steady wisdom," she wrote. "Not blood thirsty warmongering politicians trying to tweet tough by demanding assassinations."