Kentucky Republican Senator Rand Paul was walloped on Thursday by a series of media reports that concluded he was wrong to claim fellow GOP Sen. John McCain of Arizona unwittingly met with ISIS terrorists when he held a secret 2013 meeting with rebel leaders in Syria.

'Here’s the problem,' Paul told The Daily Beast on Tuesday. 'He [McCain] did meet with ISIS, and had his picture taken, and didn't know it was happening at the time.'

Paul contends that the Obama administration's effort to 'train and equip' moderate Syrian rebels against ISIS, the self-proclaimed Islamic State of Iraq and al-Sham, is foolhardy because the U.S. could wind up arming radical jihadis if alliances shift in the future.

The McCain photos, he said, show 'the quandary of determining who are the moderates and who aren’t. ... The objective evidence is that the ones doing most of the fighting and most of the battles among the rebels in Syria are the radical Islamists.'

On the Senate floor Wednesday, Paul doubled down. 'We don't even know who is in charge of the Free Syrian Army,' he said 'They voted out one guy, and in another, and he didn't even know they were voting. There are estimates that half of the Free Syrian Army has defected to al Qaeda and ISIS.'

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Sen. John McCain (center) met with anti-Assad Syrian rebels in May 2013, sparking rumors that some fighters shown with him in photos later joined forces with ISIS

Sen. Rand Paul claimed Tuesday that McCain 'did meet with ISIS, and had his picture taken, and didn't know it was happening at the time'

McCain has long been an advocate of arming rebel groups, arguing even before ISIS became a regional menace that they should have U.S. support to fight dictator Bashar al-Assad.

The Daily Beast immediately shredded Paul's claim, and a Washington Post fact-checker quickly followed suit.

Paul's office did not respond to a request for comment from MailOnline.

Central to the flap is the loyalty of the Northern Storm Brigade, a group aligned with the Free Syrian Army (FSA), a force that the Obama administration considers anti-ISIS.

Congress passed legislation on Thursday authorizing funds to train and equip FSA fighters and other moderate rebel groups.

Paul's claim has only the thinnest of evidence to support it. It was sparked by a liberal veterans' advocacy group, VoteVets.org, which claimed McCain 'paused for some photos' while in Syria, 'including some with ISIS militants.'

The claim emerged on August 19, 2014, the day ISIS released the first of its three grisly beheading videos showing the death of American photojournalist James Foley.

President Barack Obama addressed the nation Thursday night after Congress approved funding for an effort to train and arm Syrian rebel groups, a move that Rand Paul says will have unintended consequences as alliances in the Middle East shift in the future

UNCONFIRMED: Online reports claimed in August 2013 that ISIS and the Northern Storm Brigade collaborated to capture an airport from forces loyal to dictator Bashar al-Assad

A single report from the Aleppo News Network served as the basis for claims that both ISIS and the Northern Storm brigade were involved in the capture of the airport

McCain's now-famous meeting took place in May 2013 after he slipped across the Turkish border into northern Syria, meeting with rebel leaders for about an hour. Photos showed him in the company of Northern Storm leaders, who buttressed his security detail during the trip.

Three months later the Northern Storm Brigade seized an airport at the Syrian town of Mengh, completing a battle that had raged for a half-year. Twitter accounts at the time, based on reporting from the Aleppo News Network, claimed ISIS militants fought alongside them. But that has never been established.

By October, the two groups were publicly at each other's throats.

But adding to the confusion – and buttressing Paul's case – a month later the Free Syrian Army admitted to the Lebanon's Daily Star that it had joined forces with ISIS to attack Assad's forces in the Qalamoun region of Syria.

'We are collaborating with the Islamic State and the Nusra Front by attacking the Syrian Army’s gatherings,' one FSA commander told the newspaper.

'We have reached a point where we have to collaborate with anyone against unfairness and injustice,' said another.

McCain snuck into Syria from Turkey in May 2013, assisted by a rebel group called the Northern Storm Brigade -- which had an on-again, off-again relationship much later with the ISIS terror army

Mouaz Moustafa, executive director of the Syrian Emergency Task Force, a U.S.-based group that helped arrange McCain's 2013 Syria excursion but didn't choose the meeting participants, told The New York Times last week that at present, ISIS is the Northern Storm's sworn enemy.

The first issue of ISIS's glossy color magazine, Moustafa told the Times, included copies of the photos including McCain and the Northern Storm fighters along with an exhortation to 'cut all these people’s heads off.'

Shortly after the meeting, McCain spokesman Brian Rogers said that the photos were part of McCain's customary good will.

'A number of the Syrians who greeted Senator McCain upon his arrival in Syria asked to take pictures with him, and as always, the Senator complied,' he said.

As the two senators' feud deepened this week, McCain set his case back a step by misspeaking during a Fox News Channel interview, chastizing Paul for never having visited Syria himself.

'Has Rand Paul ever been to Syria?' he asked. 'Has he ever met with ISIS? Has he ever met with any of these people?'