The US and Turkey are headed for a showdown over Syria, as evidence mounts that Ankara is enabling groups that Washington is actively bombing.

Discord between the two allies is now more public than ever following a new report by Dr. Jonathan Schanzer and Merve Tahiroglu of the Foundation for Defense of Democracies.

"Bordering on Terrorism: Turkey’s Syria Policy and the Rise of the Islamic State" details Turkey's apparent willingness to allow extremists — including militants from the Islamic State (aka IS, ISIS, or ISIL) — and their enablers to thrive on the 565-mile border with Syria in an attempt to secure the downfall of Syrian dictator Bashar Assad.

"The IS crisis has put Turkey and the US on a collision course," the report says. "Turkey refuses to allow the coalition to launch military strikes from its soil. Its military also merely looked on while IS besieged the Kurdish town of Kobani, just across its border. Turkey negotiated directly with IS in the summer of 2013 to release 49 Turks held by the terrorist group. In return, Ankara reportedly secured the release of 180 IS fighters, many of whom returned to the battlefield.

"Meanwhile, the border continues to serve as a transit point for the illegal sale of oil, the transfer of weapons, and the flow of foreign fighters. Inside Turkey, IS has also established cells for recruiting militants and other logistical operations. All of this has raised questions about Turkey’s value as an American ally, and its place in the NATO alliance."

U.S. Vice President Joe Biden (L) meets with Turkey's President Tayyip Erdogan at Beylerbeyi Palace in Istanbul November 22, 2014. REUTERS/Murad Sezer Schanzer, a former counterterrorism analyst for the US Treasury Department, told Business Insider that Ankara was "like that guy at the casino who keeps doubling down on a bad bet. Each time the policy has failed, Turkey appears to have decided to go back and do it again, but with higher stakes."

Throughout the Syrian civil war, Turkey's southern border has served as a transit point for cheap oil, weapons, foreign fighters, and pillaged antiquities. As the conflict progressed, the fighters taking advantage of Ankara's lax border policies were more and more radical.

"What began with scattered opposition forces exploiting the border became something that was really focused on the Muslim Brotherhood, which then became something that was utilized by [Salafist rebel group] Ahrar al Sham, which was then utilized by [al-Qaeda affiliate] The Nusra Front, which is now utilized by ISIS," Schanzer told Business Insider.

He added that given various reports of jihadi financiers sitting in hotels on the border between Syria and Turkey, "it is impossible that [Turkey's intelligence agency] MIT is not aware" of what's going on.

The financiers "are doling out cash to those who come back with videos of attacks, proof of what they've done against the Assad regime or other enemies," said Schanzer, who previously detailed Turkey's terrorism finance problem to Business Insider. Those videos are then used as propaganda to raise more money for funding fighters.

America's Role

U.S. President Barack Obama is pictured during a joint news conference with Turkey's Prime Minister Recep Tayyip Erdogan (not pictured) in the Rose Garden of the White House in Washington, May 16, 2013. REUTERS/Jason Reed The report notes that policy of the administration of US President Barack Obama regarding Syria may have indirectly instigated Turkey's dangerous policy.

After supporting Turkey's cause of ousting Assad, Washington didn't follow up with significant support to the moderate opposition while Assad dropped Scud missiles and barrel bombs on playgrounds and bakeries.

Obama then balked at enforcing his "red line" after Assad's forces killed an estimated 1,400 people in four hours by firing rockets filled with nerve gas on rebel-held territory near the capital.

"I was in Turkey during the Ghouta attacks, and [Turkish officials] were incredulous," Schanzer said. "They believed that the United States was squarely behind [Turkish President Recep Tayyip] Erdogan, not only just in terms of steering Syria into soft landing, but also that it would back up its words with deeds and take action in light of an ongoing slaughter.

"So I think in a sense once it became clear that the US was not going to be holding to its word, there was a sense among the Turks that they had to do this themselves."

Turkish soldiers watch fighting between Kurdish fighters and Islamic State militants, from atop a hill overlooking the Syrian town of Kobani, near the Mursitpinar border crossing on the Turkish-Syrian border in Sanliurfa province November 5, 2014. REUTERS/Yannis Behrakis

ISIS And Blowback

"Turkey does not have a conflict with ISIS, doesn't want a conflict with ISIS, and ISIS is benefiting from [Turkey's] border policies," Schanzer said. "Beyond that it gets a lot more fuzzy, but the point is that the Turks are not being forthcoming about this relationship."

He added that despite no evidence that Turkey was actively working with ISIS, "it cannot be denied that Turkey is helping to facilitate the activities of a terrorist organization that has killed Americans and is destabilizing the region."

Furthermore, ISIS is gaining a following in the country. The report cites an email from Turkey-based BuzzFeed reporter Mike Giglio that highlighted his concern about the "level of ISIS support among the 1-million-plus Syrians living in Turkey. I don't see how they can successfully weed out ISIS supporters from among these refugees."

A look at the border between Turkey and Syria as of mid-September. Reuters

Schanzer said that as the suspected presence of ISIS inside Turkey increased, and with it support inside Turkey for ISIS and other extremist groups, it becomes that much more difficult for Turkey to do anything.

"They've inadvertently created a mechanism that can yield blowback for them that could be extremely painful," Schanzer said. "You have a lot of people now that are invested in the business of extremism in Turkey. If you start to challenge that, it raises significant questions of whether" the militants, their benefactors, and other war profiteers would tolerate the crackdown.

Impossible To Maintain

Tensions between Ankara and Washington won't dissipate "so long as Turkey tries to remain neutral with regard to ISIS while all of these things are happening on its border," according to Schanzer.

Consequently, the report argues, Washington must find a way to work with Turkey. Outgoing Defense Secretary Chuck Hagel described Turkey as "absolutely indispensable" to the ISIS fight. Turkey would need to shut down the border, wrap up known nodes of Nusra and ISIS supporters, remove ISIS recruitment cells, and dismantle ISIS logistical operations inside the country. (Schanzer noted that the US or NATO could assist.)

Turkey's President Recep Tayyip Erdogan listens during a news conference in Riga October 23, 2014. REUTERS/Ints Kalnins "A lot of this is going to come down to the will of Ankara right now," Schanzer said, adding that a lack of cooperation could result in Treasury Department sanctions against "individuals who are taking an active role in these illicit pipelines" on the Turkish side of the border.

"After that, I think we do begin to question whether security or intelligence cooperation can continue when there isn't an honest give and take with what's happened," Schanzer added.

The report concludes that Ankara must understand that "while America's Syria policy may have been feckless, its border policy has been reckless." And the repercussions of doubling down even further would jeopardize relations with a crucial ally.

"No one wants to scuttle this relationship. But I do think that as more and more of this comes to light, it becomes ... essentially impossible to maintain the status quo," Schanzer said. "If we've decided that ISIS is an enemy worth defeating, it becomes impossible to maintain the relationship as it is."