Trump’s decision to pull out of Syria has sent Turkey, Russia and Iran scrambling to find a solution for the northeast.

On February 14, leaders of the Astana process – Russia, Iran and Turkey – held a trilateral summit in the Russian Black Sea resort, Sochi, for the first time since US President Donald Trump announced his intention to withdraw US troops from Syria last December.

Three issues dominated the talks: first, what should happen to the opposition-held Idlib province and the demilitarised zone; second, how the Astana process partners should respond to the US decision to withdraw from northeastern Syria without having their interests clash and their cooperation collapse; and third, how to move forward on the formation of a constitutional committee, which is considered a key step towards a political solution.

Taken together, these three issues constitute the biggest challenge to the Astana process since its inception two years ago.

The future of Idlib

For many years, Russia, Iran and Turkey were bitter rivals in the Syrian civil war, supporting different sides in the conflict. Russia and Iran backed the Syrian regime, providing military, financial and political support, while Turkey assisted the Syrian opposition and provided a safe haven for its political and military leadership.

The relationship between Turkey and Russia, in particular, reached its lowest point in November 2015 when Turkey downed a Russian fighter jet near its border with Syria. Relations improved, however, when both Iran and Russia condemned the July 2016 coup attempt in Turkey, expressing sympathy for President Recep Tayyip Erdogan, who felt increasingly ostracised by his Western allies.

Rapprochement with Russia enabled Turkey to launch its first large-scale military operation inside Syria called Euphrates Shield in August 2016, wherein Turkish troops and Turkey-backed Syrian opposition factions recovered more than 2,000 square kilometres from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) and the Syria Democratic Forces (SDF) on the western bank of the Euphrates near the Turkish border. The fall of Aleppo, which came a couple of months later, allowed Russia and Turkey to identify common interests in Syria. This led to the launching of the Astana process in January 2017, which Iran joined later.

In 2017, Astana allowed for the establishment of the so-called de-escalation zones in four major areas of conflict between the Syrian regime and the opposition: in Idlib province, in Northern Homs province, in Eastern Ghouta, near Damascus, and in Deraa and Quneitra provinces. Russia used the de-escalation mechanisms to freeze the conflict with the opposition so that it could commit more troops in the race with the US for the control of ISIL-held territories in Syria’s vast and resource-rich eastern provinces.

In 2018, it resumed its offensive against the Syrian opposition, expelling them from three of the four de-escalation zones. In light of major differences with Turkey and Iran’s opposition, Russia spared Idlib.

A bilateral agreement between Erdogan and his Russian counterpart Vladimir Putin was reached in September 2018, just 10 days after the failure of a three-way summit in Tehran. The agreement allowed for the establishment of a 15-20km deep demilitarised zone in Idlib. In return, Turkey pledged to disarm and remove from the area Hay’et Tahrir al-Sham (HTS) – a rebel group that was previously affiliated with al-Qaeda, which Russia considers a terrorist organisation.

However in January 2019, fearing the collapse of the Russia-Turkey agreement on Idlib after the announcement of the US withdrawal, HTC acted preemptively, taking control of most of the Idlib province. Russia considered the move by HTC a violation of the 2018 agreement.

At Thursday’s Sochi summit, Turkey tried to buy more time to solve the issue in Idlib and prevent an attack that could drive most of the three million refugees living in Idlib towards Turkey. Russia, which attaches great importance to Turkey’s cooperation in Syria, especially at the current state of uncertainty about US policy, does not seem in a hurry to mount an attack in Idlib.

One can, therefore, say that the Russian-Turkish understanding of Idlib will hold until at least the picture in northeastern Syria becomes clear.

The US withdrawal

US President Donald Trump‘s decision to pull out his troops from Syria by April was a major source of tension at this week’s summit. Previously, Turkey, Russia and Iran stood united in their opposition to the policy former Secretary of State Rex Tillerson had outlined to keep US troops after the defeat of ISIL in Syria to curb Iranian influence.

The sudden switch must have taken all three by surprise and major differences seem to be emerging within the troika.

Thus, Trump’s decision should be seen as the most important development in the Syrian conflict since the Russian intervention in September 2015. It is likely to have just as much effect on the course of the conflict both on the ground and internationally.

One important point of disagreement between Turkey, Russia, and Iran has been who should inherit the territories held by US allies – the SDF. Turkey’s paramount concern in Syria has always been the Kurdish question. Its ultimate objective is to eliminate the threat posed by the SDF, which is dominated by the Kurdish People’s Protection Units (YPG), armed and trained by the US to fight ISIL. The Turkish government sees the YPG as the Syrian branch of the Kurdistan Workers’ Party (PKK) and considers it a terror group.

It has demanded from the US to disarm it before it withdraws and has proposed a “buffer zone” 30km into Syrian territories along its 450km border with Syria east of the Euphrates. Ankara has already established a “safe zone” on the western bank of the Euphrates through its August 2016 Euphrates Shield and early 2018 Olive Branch operations.

Russia and Iran have completely different visions of what should happen in the US-dominated area. They have suggested that the SDF-held territories should go back under the control of the Syrian regime. Russia seems willing to entertain the Turkish proposal only if it is implemented in coordination with the Syrian regime.

To that end, it has suggested that Turkey and Syria reactivate the Adana Accord of 1998, which allows the former to pursue PKK fighters inside Syrian territories but not to establish permanent military presence.

Moscow’s ultimate objective here is to push Ankara to recognise the Syrian regime as the legitimate government of Syria and deal with it as such. If it succeeds in achieving this goal, that could be a game changer in the Syrian conflict.

However, nothing of that sort can happen until US plans and post-withdrawal arrangements become clear. If the US decides to coordinate its withdrawal with Turkey that would put the Turks in a much better position vis-a-vis the Russians and the Iranians and at the same time push the YPG closer to the Syrian regime camp.

If the US decides not to coordinate with Turkey, Iran and Russia will take advantage and try to fill in the void, leaving their Astana partner in a much weaker position and with no option but to accept the offer of returning to the Adana Accord.

The constitutional committee

The Astana process has so far allowed Russia to achieve two key objectives in its Syria crusade: defeat the opposition militarily and shift the focus in the political process from political transition to an amendment of the constitution.

In January 2018 and with the help of Turkey, Russia hosted the Syrian Congress of National Dialogue in Sochi. The event brought together representatives from the Syrian regime and parts of the Turkey-based opposition.

Its main objective was to set the stage for the launching of the constitutional committee. Former UN Special Envoy to Syria Staffan de Mistura also attended the meeting where an agreement was charted between him and the Russians to form a committee to rewrite the Syrian constitution and end the conflict.

The committee is supposed to have 150 members: 50 proposed by the Syrian regime, 50 by the opposition and 50 by the United Nations, to include representatives of civil society and technical experts.

Since then, this last third has become a key point of contention between the Astana partners, as each has tried to influence the selection of the names in this list, which could tip the balance in favour of the regime or the opposition. After almost a year of arms twisting, some progress seems to have been made but no final agreement has been reached so far.

It is also not clear what the US response would be to the formation of the constitutional committee. Its official position has always been to back the UN-led Geneva peace negotiations and reject any attempt by Russia to dictate the terms of the political solution in Syria. However, with Trump ordering the withdrawal of US troops, it is unclear whether his lack of interest in Syria extends to the future of the political process as well.

One thing, however, is for sure: the US president dislikes the Astana trio. He would want to see it disbanded and this might as well happen. His decision to withdraw has caused major fractures to appear in this already unstable alliance.

In the end, whatever Russia, Iran and Turkey try to do in Syria, it will always be contingent on the US finally making a decision on whether and how to exit this eight-year-long deadly conundrum.

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial stance.