As reported by Censor.NET citing CNN, the Arizona Republican was speaking about Russian critic and deputy leader of the Freedom Party Vladimir Kara-Murza, who's recently been hospitalized in Russia. His lawyer believes he was poisoned.
"Vladimir knew that (Russian President Vladimir) Putin is a killer. And he's a killer. And he might very well be the next target. Vladimir knew there was no moral equivalence between the United States and Putin's Russia," said McCain, who's long been a fierce critic of Trump's rhetoric about Russia.
"I repeat," he continued, veering away from his prepared remarks and hitting the wooden lectern to underscore his point. "There is no moral equivalence between that butcher and thug and KGB colonel and the United States of America, the country that Ronald Reagan used to call a shining city on a hill. And to allege some kind of moral equivalence between the two is either terribly misinformed or incredibly biased. Neither can be accurate in any way."
McCain listed a number of other Putin critics and journalists who've allegedly been killed by the Russian government.
While he didn't mention Trump by name, his comments came just days after Trump appeared to argue in an interview with Fox News' Bill O'Reilly that the United States had killed people in the same manner as Russia.
"Putin's a killer," O'Reilly said in the interview.
"We've got a lot of killers," Trump said. "You think our country's so innocent?"
When O'Reilly pushed back, saying he doesn't know any U.S. government leaders who are killers, Trump cited the Iraq War and said "we've made a lot of mistakes."
"A lot of mistakes -- OK -- but a lot of people were killed," Trump said. "So a lot of killers around, believe me."