McCain's comments came after Paul objected to a resolution that would allow Montenegro to join the NATO alliance. McCain responded by lobbing accusations at his fellow GOP senator multiple times, both before and after Paul objected to the vote, though the Kentucky senator did not add additional defense Wednesday.
Pointedly singling out the "gentleman from Kentucky," McCain said those who object "are now carrying out the desires and ambitions of Vladimir Putin."
When Paul formally objected, McCain reiterated his opinion.
"The senator from Kentucky is now working for Vladimir Putin," he said.
The sharp attack had some congressional observers wondering how McCain hadn't violated Rule 19, as the GOP said Sen. Elizabeth Warren had when she criticized former-senator-now-Attorney-General Jeff Sessions earlier this year.
Warren was halted from speaking after Senate Majority Leader Mitch McConnell called her out of order
-- citing Rule 19 -- for allegedly impugning a fellow senator. Warren was reading a decades-old letter by Coretta Scott King condemning Sessions ahead of his attorney general nomination vote.
The unusual scene shocked many and turned into a quasi-movement
on the left unified by one rallying cry. It came from a letter released by McConnell describing the invocation of the rule, saying that Warren "was warned. She was given an explanation. Nevertheless, she persisted."
Neither the offices of Paul nor McConnell responded immediately to CNN requests for comment.
"I think John McCain violated Rule 19 on Rand Paul. ... So do these accusations violate the Senate rule against impugning another senator?" Roll Call reporter Niels Lesniewski tweeted
, to which, Paul adviser Doug Stafford responded "See you in court" in a tweet
written in Russian.
Rule 19 of the Senate rules states, "No senator in debate shall, directly or indirectly, by any form of words impute to another Senator or to other Senators any conduct or motive unworthy or unbecoming a Senator."
When asked about whether he thinks he violated Rule 19, a spokeswoman for McCain nevertheless persisted in focusing on Paul's vote on Montenegro.
"Sen. McCain believes that the person who benefits the most from Congress' failure to ratify Montenegro's ascension to NATO is Vladimir Putin," Julie Tarallo, a McCain spokeswoman, told CNN. "The senators who support this treaty, and certainly the people of Montenegro, deserved an explanation from Sen. Paul."
After the harsh words were exchanged on the Senate floor, Montenegro's Ambassador to the US, Nebojsa Kaludjerovic, told CNN that while it's obvious that "Sen. Paul still objects to the resolution," what is "most important is that at least 98 senators are in favor of it." The ambassador said the "key now is finding the time to vote" and he hopes "it might be done soon."
The Pentagon sides with McCain and is also in favor of Montenegro's membership. A spokesperson from the Department of Defense said that they "continue to support Montenegro's NATO membership," and added that "ratification of Montenegro's accession will be an important reminder of this commitment."
Rule 19 is open to interpretation by Senate members, and its invocation is up to the senators and the member presiding. It's notable that after it was invoked against Warren the Senate Historian's Office scrambled to determine when it was last enforced. They were not able to provide a definitive count of the times it's been used.