Sen. John McCain, R-Ariz., on Wednesday accused Sen. Rand Paul, R-Ky., of "working for Vladimir Putin" after Paul blocked consideration of a treaty that would allow Montenegro into NATO.

McCain tried to call up the treaty and warned that anyone blocking it would be helping Russia maintain its influence over the small country across the Adriatic Sea from Italy.

"If there's objection, you are achieving the objectives of Vladimir Putin," McCain warned. "If they object, they are now carrying out the desires and ambitions of Vladimir Putin, and I do not say that lightly."

But as predicted, Paul quickly objected with McCain asked for consent to call up a resolution that would have the U.S. ratify the treaty if approved.

"I object," Paul said before quickly leaving the Senate. Paul's move shocked McCain, who said Paul didn't appear to have any good reason for objecting.

"That is really remarkable," McCain said. "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."

"The only conclusion you can draw when he walks away is he has no argument to be made," he said.

"The senator from Kentucky is now working for Vladimir Putin," McCain concluded.

Paul released a statement after the incident that said the huge and growing national debt is why the U.S. should not take on any additional commitments around the world.

"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)," Paul said. "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," he said.

A spokeswoman for McCain said Paul's explanation isn't enough, and that he should have offered one to the chamber as he objected to McCain's request.

"The overwhelming majority of senators who support this treaty, and certainly the people of Montenegro, deserved an explanation from Senator Paul on the Senate floor as to why he sought to prevent this small, brave country from joining in the defense of the free world," said spokeswoman Julie Tarallo.

This story was corrected to note that the issue is Montenegro's admission into NATO, not the United Nations.