JOHN MCCAIN: Rand Paul Doing 'Somersaults As These Beheadings Took Place'

Sen. John McCain (R-Arizona) tore into Sen. Rand Paul (R-Kentucky) on Tuesday, accusing him of "desperation" and of sliding "down a very steep slope of credibility" on foreign policy issues.

"I think it's a fundamental lack of understanding of the situation and the threats we face. Sen. Paul has obviously been doing some somersaults as these beheadings took place and the American people's opinion has shifted rather dramatically," McCain said in a Fox News interview.

Paul, a potential 2016 presidential candidate, has faced a storm of criticism over his seemingly evolving stance on military action against the Islamic State, also known as ISIS. The group gained international notoriety after beheading two American journalists earlier in the summer.

Paul has criticized "interventionists" in the White House for the the rise of ISIS, but later claimed he "would have acted more decisively and strongly" to combat the group than Obama. McCain, a fairly consistent advocate of aggressive military action abroad, seemed amused.

"He has dramatically shifted his positions on national security," McCain said. "I don't think he understands the nature of the threat. And I don't think he understands how serious it is."

McCain also sharply criticized Paul for suggesting he met with Islamic State officials - a claim the Daily Beast described on Wednesday as "proven false."

"He's even said that I met with ISIS which is a patently false [accusation]. In fact, ISIS called me the No. 1 enemy when I went to Syria," McCain said. "So I think it's kind of a desperation, trying to find some footing here as he slides down a very steep slope of credibility."

Business Insider reached out to Paul's office earlier this week after the senator was accused of flip-flopping by Democrats and Rep. Peter King (R-N.Y.). In response, a top staffer insisted Paul has maintained a "consistent" position on military intervention in the Middle East.

"Senator Paul has been consistent," the staffer, Doug Stafford, said. "He pushed to stop the foolish drive toward war on the side of ISIS last year, recognizing the radical jihadists in the region posed the greatest threat to the United States. He opposed arming any rebels."

View the McCain interview below.