What will change if the Islamic State and al-Qaida patch things up?

Syrian opposition officials say the Islamic State has reached a truce with its erstwhile partners in al-Qaida. The accord apparently took place at a meeting in northern Syria last week that involved members of ISIS, al-Qaida's Syrian affiliate Jabhat al-Nusra, and members of the Khorasan Group, a group of al-Qaida veterans from Pakistan and Afghanistan who have embedded with Nusra.

According to the AP, these opposition officials say the jihadi groups "agreed to work to destroy the Syrian Revolutionaries Front, a prominent rebel faction armed and trained by the United States and led by a fighter named Jamal Maarouf." Some details of the meeting had been reported earlier this week by the Daily Beast's Jamie Dettmer, who wrote that moderate Syrian rebel groups "accuse the Obama administration of fostering jihadi rapprochement" through the airstrikes it launched against Nusra in the early days of the intervention. Those strikes were billed as a bid to take out the members of Khorasan - a group that few fighters on the ground in Syria seemed to have heard of until recently.

U.S. officials haven't confirmed the report of a merger and tell the AP they've seen no shifts in the two groups' strategies.

If it's real, the merger will shift the dynamics of the very complex battlefield in Syria. Up until now, ISIS didn't really have any friends in the region, even among groups that largely share its ideology. Between this and Egyptian militant group Ansar Beit al-Maqdis' pledge of support this week, it's possible that ISIS is starting to get more respect from fellow jihadi groups. It would also be quite a reversal for al-Qaida leaders, who disavowed their renegade Iraqi faction months ago.

The AP's Deb Riechmann writes that the accord would "present new difficulties for Washington's strategy," which is true, though in some ways it would make things simpler. The line between the U.S.-backed "moderate" rebels and the anti-ISIS Jihadist groups was always more fluid than anyone wanted to admit.

In his recent account of his months of captivity in Syria, journalist Theo Padnos recalls a conversation he had after running into a group of Free Syrian Army troops while he was still a captive of al-Nusra.

1/8begin ital 3/8 One told me that his unit had recently traveled to Jordan to receive training from American forces in fighting groups like the Nusra Front.

"Really?" I said. "The Americans? I hope it was good training." "Certainly, very," he replied.

The fighters stared at me. I stared at them After a few moments, I asked, "About this business of fighting Jebhat al-Nusra?" "Oh, that," one said. "We lied to the Americans about that." 1/8end ital 3/8 The White House never bought the "enemy of my enemy" logic when it came to ISIS and Nusra - it's been bombing both of them, after all. This merger, along with growing signs that Washington is resigning itself to Bashar Assad's long-term presence, could be an indication that the overlapping and intersecting battle lines in Syria are starting to clarify themselves. At the moment, the U.S., the Kurds, Iraqi Shiites and - whether the Obama administration will admit it or not - the Syrian government are on one side, and ISIS and al-Qaida are on the other.

The big loser in all of this is likely to be the U.S.-backed rebels. In addition to ISIS and Nusra finding common cause, there are reports this week that the White House is considering revamping a Syria strategy many senior officials have come to see as unworkable. That strategy, which involved focusing primarily on rolling back ISIS in Iraq and didn't involve strikes against Assad, never sat well with the rebels. A new one, which could involve a new diplomatic push for a cease-fire deal whose terms would likely be very disadvantageous to the Syrian opposition, would be even worse.

At the moment, as they wait to see how things play out, America's friends in Syria are finding themselves stuck in a very uncomfortable middle.

Keating is a staff writer at Slate focusing on international news, social science and related topics. He was previously an editor at Foreign Policy magazine.