The first obstacle is that the United States and Russia still have significantly different positions on key issues, most notably on President Bashar al-Assad. While the Obama administration appears to have retreated somewhat, at least in practice, from the president’s August 2011 declaration that “the time has come for President Assad to step aside,” Washington still wants the Syrian leader’s departure as a guaranteed outcome of any political settlement. Moscow is comfortable with Assad’s eventual removal, but sees him and his regime as the only currently viable potential basis for a stable government in the country.

These statements, and renewed modest goodwill between Washington and Moscow, do seem to provide another chance to work together on Syria. That said, achieving results — rather than simply “opening a dialogue” — will be quite challenging.

At the same time, each side has drawn particular attention to the related problems of Syria and the Islamic State (IS) in reporting on their dialogue and assessing the future. In his news conference on the Iran agreement, Obama said, “We’re not going to solve the problems in Syria unless there’s buy-in from the Russians, the Iranians, the Turks, our Gulf partners,” adding, “There’s going to have to be agreement among the major powers that are interested in Syria that this is not going to be won on the battlefield.” Russian Foreign Minister Sergey Lavrov expressed optimism that “the largely artificial obstacles to forming a broad coalition in the fight against the Islamic State and other terrorist groups are being removed.”

The Iran deal has produced a level of mutual congratulations in the US-Russia relationship that, however mild, has not existed for some time. According to the White House, President Barack Obama “thanked President [Vladimir] Putin for Russia’s important role in achieving this milestone” during a July 15 telephone conversation. Two days later , the Kremlin announced that Putin and members of Russia’s Security Council — including Russia’s top military, intelligence and security officials, who are generally not Washington’s best friends in Moscow — “noted again that the leading role and constructive position taken by the United States played a big part in making it possible to finalize the agreements” during a meeting chaired by Putin. This ritualistic exchange of praise was quite different in tone from many other recent statements from the two governments.

Will the success of US-Russian cooperation in reaching a major agreement on Iran’s nuclear program create a new opportunity — and new momentum — for a political solution to Syria’s seemingly unending civil war? Both Washington and Moscow appear to be leaving the door open. But walking through it will not be easy.

Related to this, Russian officials are also clearly quite reluctant to attempt to persuade Assad to take a deal with a foreordained outcome that Assad himself is likely to find very unattractive. And they don’t think it will work anyway. Conversely, even if the Obama administration agreed to give up on “guarantees” that Assad would depart as a component of a settlement, the White House would face withering political criticism at home for doing so — from Democrats as well as Republicans.

Moreover, any such understanding would not occur in a vacuum. It would occur after an Iran deal that has already been controversial domestically and with US allies in the region, including both Israel and America’s Gulf Cooperation Council partners. In this context, it is essential to recall that Obama has acknowledged that not only Moscow, but also Tehran, would have to “buy in” to a Syria settlement for it to work. That means Iran would have to take part in the process in some way. And it means that any result that doesn’t include Assad’s immediate removal would look like a concession not only to Russia, but also to Iran — after what many (justifiably or not) see as major concessions having been made in the nuclear deal and in an environment where US allies fear an American strategic realignment that could privilege Iran’s interests at their expense. In short, a political settlement in Syria on the only possible terms would confirm the worst fears of some of Obama’s political opponents as well as key US allies. The White House surely knows this.

The barriers to the more limited undertaking of US-Russian cooperation against IS (as opposed to joint efforts to solve the Syrian problem) are less formidable, though still significant. Here, one of the most significant is Moscow’s long-time insistence that the United States and others cannot conduct airstrikes in Syria without permission from Damascus. Of course, this does not prevent collaboration in supporting the Iraqi government, which Russia has already supplied with weapons.

An interesting question is whether Washington and Moscow might be able to find a creative solution to the “permission” problem. In discussing Iran’s role in fighting IS forces in Iraq, Obama has essentially delegated to Baghdad the responsibility to “de-conflict” US and Iranian military operations because Washington is not able to do this directly. With this in mind, could Moscow play a similar role by “de-conflicting” US and Syrian military operations against IS?

In theory, this is not too different from what Obama is already prepared to accept (and even to acknowledge publicly) in Iraq. Still, there are two big problems with this idea. One is that any tactical coordination with Damascus (which would be almost impossible to keep secret in the United States) would inherently help the Assad regime in its fight against all its opponents and not just IS. Even indirect and loose coordination through Moscow could allow the Syrian government to redeploy its forces to take advantage of known US operations. Like concessions to Iran, this is political poison in Washington.

Second, taking this approach would amount to sharing sensitive information on ongoing US military operations with Russia at a time when the US and Russian militaries are increasingly reorienting toward confrontation with one another. For its part, in any such dialogue the United States might ask for details about Russian arms shipments to Syria — also sensitive and a source of contention. Discussions like this would not be easy at all.

Even before the Ukraine crisis, less-ambitious counterterrorism cooperation foundered for years due to lingering mutual mistrust between intelligence and security agencies. For example, Russia repeatedly warned the US FBI about Tamerlan Tsarnaev, a Chechen immigrant to the United States who Moscow saw as a terror risk as early as two years before Tsarnaev and his brother executed the 2013 Boston Marathon bombing. FBI officials distrusted Russia’s motives and did not aggressively pursue the lead.

Objectively, both the United States and Russia have similar interests in Syria: ending the war, defeating IS and stabilizing Syria and its neighbors. Unfortunately, that is not always enough to produce cooperation between major powers.