Monday's announcement by the United States and Russia of a so-called "cessation of hostilities" in Syria is the second such proposal in as many weeks. The first proposal for a cessation of hostilities ended last week before it even began. But if all goes to plan, the fighting in Syria will stop, or at least be drastically reduced, starting on midnight Saturday, February 27.

Do not hold your breath.

How the cessation of hostilities will work in practice, and how it will turn into a more permanent ceasefire in war-torn Syria, remains to be seen.

Who is a terrorist?

The so-called International Syria Support Group (ISSG), a group of international countries and organisations hoping to bring a resolution to the civil war, has been given the task of finding a consensus on what constitutes a terrorist group in Syria.

However, beyond identifying ISIL and al-Nusra Front as terrorist organisations, there is little consensus among the ISSG.

This lack of consensus on which groups fighting in Syria are terrorist organisations will be the loophole that allows Russia to continue its support for Assad's military offensive in places around Aleppo.

READ MORE: Aleppo can be a turning point in Syria's civil war

It will also be the loophole that will allow Turkey to continue shelling the Kurdish People's Protection Units, or YPG.

Perhaps the single biggest limiting factor for an enduring cessation of hostilities in Syria is the fact that the two external power brokers, the US and Russia, have neither credibility nor clout in the region.

Perhaps the YPG is the best example of how chaotic the situation on the ground has become in Syria. The YPG is the armed wing of the Syrian Kurdish group the Democratic Union Party or the PYD.

The YPG is simultaneously: fighting and making gains against ISIL and other rebel groups in Syria, being attacked by US-ally and Russian-adversary Turkey, fighting Russian-backed Syrian forces, and is being armed by both the US and the Russians. Not confusing enough?

In the case of the YPG, the US and Russia are essentially fighting proxy wars against themselves. It would be farcical if the situation wasn't so serious.

No credibility

As if the impasse over agreeing over the terrorist list were not bad enough, perhaps the single biggest limiting factor for an enduring cessation of hostilities in Syria is the fact that the two external power brokers, the US and Russia, have neither credibility nor clout in the region.

US influence in the Middle East is at its lowest point in decades. Look at the way US President Barack Obama handled the drawdown from Iraq in 2010, Washington's relations with Israel, and the flawed Iran deal which left America's Gulf allies out to dry.

The sum of these policy decisions has left US commitment open to question and US influence diminished across the region.

Russia, on the other hand, has zero credibility at implementing past ceasefires. Almost seven years later Moscow is still in direct violation of the six-point ceasefire plan that ended its five-day invasion of the Republic of Georgia.

The so-called Minsk II ceasefire agreement in eastern Ukraine is violated every day by Russian-backed separatists. Moscow regularly eggs on both Azerbaijan and Armenia over the latter's occupation of Nagorno-Karabakh by selling both sides in the conflict billions of dollars' worth of weaponry.

When it comes to supporting ceasefires, Russia has a dismal record. Why would Syria be any different?

Pure fantasy

The idea that a cessation of hostilities in Syria can be enforced is pure fantasy. There is no political will for an international peacekeeping force. There is not even consensus on something as basic who is a terrorist and who us not.

READ MORE: Putin declares checkmate on Syria

Turkey will continue striking the YPG. Russia will continue striking the many Salafist Sunni groups fighting against the Assad regime. The US and Europe will continue pretending there is a cozy moderate third option to support between Assad on the one hand and groups such as ISIL on the other.

The brutal truth is that the civil war has been left to rot and fester for so long that there is very little the US or even Russia can do to engineer a cessation of hostilities, much less a full-blown ceasefire, armistice or peaceful outcome.

Last-minute push

A year ago, during the so-called Mink II ceasefire negotiations, a battle was raging over control of a Ukrainian city and strategic railroad junction called Debaltseve.

A ceasefire was finally agreed for February 15 - but the Russian-backed separatists had unfinished business in Debaltseve and continued fighting until they captured the city on the 18th.

The upcoming cessation of hostilities in Syria will be no different.

Between now and February 27, Russian-backed Syrian forces will make a last-minute push on Aleppo. If Syrian forces cannot mop up the defenders of Aleppo (many of whom, by the way, are far from being the "moderates" talked about so much in the Western media) by this Saturday, then Moscow will use its "terrorist loophole" to continue the air strikes.

The proposed cessation of hostilities is not worth the paper it's written on. Sadly for the innocent civilians caught in the fighting, the killing is likely to continue.

Luke Coffey is a research fellow specialising in transatlantic and Eurasian security at a Washington DC-based think-tank. He previously served as a special adviser to the British defence secretary and was a commissioned officer in the United States Army.

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