'The senator from Kentucky is now working for Putin': John McCain slams Rand Paul for blocking Montenegro from joining NATO

Republican Sen. John McCain slammed his GOP colleague, Kentucky Sen. Rand Paul, on Wednesday after Paul blocked the passage of a treaty that would allow Montenegro to move forward with joining NATO, Defense News' Joe Gould reported on Wednesday.

"The senator from Kentucky is now working for Putin," McCain said after Paul entered the Senate chamber, voted against the accession protocol, and exited.

"@SenJohnMcCain, @SenatorShaheen @BenCardinforMD clearly unhappy Paul abruptly walked out without any rationale or debate," Gould tweeted.

McCain seemed to be implying that Paul's move to block the treaty aligned with Russian President Vladimir Putin's staunch opposition to Montengro's accession to NATO, which he views as a threat to Russian sovereignty. Albania and Croatia joined the alliance 2009.

For Montenegro to move forward with the accession process, which was approved in May, the treaty has to be ratified by the US Senate by unanimous consent. Twenty-one of 28 NATO allies have already backed Montenegro's accession.

Asked about McCain's comment, Paul stood by his decision to block the treaty and said it would be "unwise to expand the monetary and military obligations of the United States given the burden of our $20 trillion debt."

"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 told Business Insider in a statement provided by his office. "In addition, the United States is pledged to defend 28 countries in NATO."

McCain, meanwhile, has said he would "love to see" Montenegro join NATO and promised Montenegro Prime Minister Dusko Markovic in January that the Senate would ratify the treaty soon, according to Radio Free Europe.

Markovic was the target of a coup plot, allegedly orchestrated by Russian intelligence agents, to overthrow Montenegro's pro-NATO government and replace it with a Russia-friendly regime, The New York Times reported. The plot was uncovered in November after the pro-Russian mercenary who helped organize it was arrested by Montenegrin police.