The long-simmering war between Sens. John McCain and Rand Paul boiled over on Wednesday when the Arizona lawmaker directly accused his colleague of working for Russian President Vladimir Putin.

While speaking from the Senate floor in support of a bill advancing Montenegro’s bid to join the North Atlantic Treaty Organization (NATO), McCain noted objection from his Kentucky colleague, saying that if you oppose the measure, “You are achieving the objectives of Vladimir Putin... trying to dismember this small country which has already been the subject an attempted coup.”

McCain continued: “If they object, they are now carrying out the desires and ambitions of Vladimir Putin and I do not say that lightly.”

Several moments later, after the 80-year-old senator asked for unanimous consent to move the bill forward, Paul took the mic to raise his objection before dramatically exiting the room.

In response, McCain began railing against Paul, his voice trembling with anger: “I note the senator from Kentucky leaving the floor without justification or any rationale for the action he has just taken. That is really remarkable, that a senator blocking a treaty that is supported by the overwhelming number—perhaps 98, at least, of his colleagues—would come to the floor and object and walk away.”

He then directly connected Paul to the Russian government: “The only conclusion you can draw when he walks away is he has no justification for his objection to having a small nation be part of NATO that is under assault from the Russians.

“So I repeat again, the senator from Kentucky is now working for Vladimir Putin.”

In a statement to The Daily Beast, a McCain spokesperson clarified the senator’s words, writing: “Senator McCain believes that the person who benefits the most from Congress’s failure to ratify Montenegro’s ascension to NATO is Vladimir Putin, whose government has sought to destroy the NATO alliance, erode confidence in America’s commitments to its allies, overthrow the duly-elected government of Montenegro, and undermine democratic institutions throughout Europe.”

His office further stated: “Senator McCain, and certainly the people of Montenegro, would appreciate an explanation from Senator Paul as to why he sought to prevent this small, brave country from joining in the defense of the free world.”

In response, Paul avoided the over-the-top nature of McCain’s initial attack, instead commenting on the policy issue at hand. “Currently, the United States has troops in dozens of countries and is actively fighting in Iraq, Syria, Libya, and Yemen (with the occasional drone strike in Pakistan),” he told The Daily Beast.

“In addition, the United States is pledged to defend 28 countries in NATO. It is unwise to expand the monetary and military obligations of the United States given the burden of our $20 trillion debt.”

Paul’s NATO-skeptic words notably echo those of President Trump, who ran on backing away from involvement with the alliance, having called it “obsolete” and lamented how it “costs us a fortune.” McCain, of course, vehemently opposed such words.

The Arizona senator’s brusk accusation is the latest controversy to emerge from the Senate floor. Little more than a month ago, Majority Leader Mitch McConnell cut off Democratic Sen. Elizabeth Warren as she read a 1986 letter from Coretta Scott King suggesting Sen. Jeff Sessions actively worked to block the black vote.

Citing a Senate rule against impugning the motive of a colleague, McConnell reprimanded Warren. The majority leader’s office did not immediately respond to request for comment on whether McConnell plans to similarly punish McCain for suggesting his colleague works for the Russian government.