It was on Wednesday that Donald Trump sent that fateful tweet about a looming attack on Syria as punishment for the latest use of chemical weapons by the Assad regime. My judgment, before then, was that western military action was not, necessarily, part of the answer to the conflict. Needed, instead, was political will on the part of the US in particular – as the only superpower able to exert serious pressure on the main broker in Syria, Russia – to bring the warring sides to the negotiating table.

But once Trump had declared that he would punish Bashar al-Assad militarily, he had to follow through – not doing so would have destroyed US credibility. The use of chemical weapons in Douma showed that Trump’s 49 missiles launched on regime targets last year in retaliation for the chemical attack in Khan Sheikhun did not deter Assad from repeating the act. And a similar one-off limited attack is not going to achieve much.

The truth is that military punishment on its own, no matter the scale, will not end the conflict. The survival both of pro-Assad forces and rebels (despite changes in the composition of the two camps) after seven years of conflict shows that no entity can win the Syrian war militarily.

But that’s not the same as wishing the Syria conflict away by saying it’s too late to do anything, as has become increasingly tempting for some in the west to say, especially given that the Assad regime appears to be taking back areas from rebels across Syria. Letting the regime win, the “do nothing” argument goes, is not ideal but at least it would bring stability to Syria. Such an argument is not only misguided but dangerous. No conflict in history ever reached the point of “too late to do anything” about. And doing nothing in the case of Syria simply means allowing one phase of the conflict to end while paving the way for something even bloodier in the future.

However, what can be done about Syria has changed over the past seven years. In the very beginning, before the crisis turned into a war, it would have been possible to use international diplomacy both to pressure and coax the Syrian regime to give some concessions to protesters. But there was no political will among western countries to do so.

When the conflict turned bloody and it became clear that Assad was picking up where Libya’s Muammar Gaddafi left off – reacting violently to anti-regime protests – it would have been possible to remove him through military action, especially since Russia and Iran’s role in supporting Assad at the time was still nascent. But the experience of Libya in 2011 and of Iraq in 2003 meant there was no appetite in the west for military intervention in Syria, even though the three contexts were not identical. This led Assad to dismiss calls for him to step down as mere rhetoric.

Barack Obama’s empty “red line” warning about the use of chemical weapons in 2013 further weakened the credibility of the US in particular and the west in general as far as the Assad regime was concerned. It has continued to use chemical weapons as a tactic to force rebels and civilians out of strategic areas it wants to take over without fear of accountability. But even if the regime extended its control all over Syria, rebel groups would continue to operate, causing instability similar to that witnessed in Iraq intermittently since 2003. Equally, if the insurgents somehow pushed back against pro-Assad forces and began taking over regime strongholds such as Damascus and the west coast, pro-regime forces would not simply give up.

All this shows that the only way for the conflict to end remains through a political process to bring about a transition in power, which demands that the US develops a political strategy for Syria. Now that the US has committed to military action, attacks can only be a means to an end, the route to putting enough pressure on Russia to convince it to agree to serious negotiations.

Serious negotiations mean declaring the Astana process and Sochi talks dead and abandoning the facade that Russia became adept at exhibiting during the Geneva process. For Russia to behave seriously in negotiations, it has to believe that the US is serious. What works in favour of the US is that its key allies – the UK, France and Saudi Arabia – are all aligned. This gives it a unique opportunity to engage in a sustained, targeted campaign against Assad’s military assets that has wide international endorsement.

Though there are suggestions that last week’s attack might be a one-off, such a campaign would ideally not be halted until Russia agrees to serious talks on political transition in Syria. Ultimately, Russia does not want its foothold on the Mediterranean to be composed of rubble.

It should not be forgotten that, in the end, chemical weapons are not the main problem in Syria – they are the symptom of the real problem, which is the Assad regime in power. It is this regime that authorised the use of these weapons in the first place. But there is no point in deterring Assad from using chemical weapons while continuing to allow him to use conventional weapons against civilians and to engage in activities such as unlawful imprisonment and torture.

There is still a way out of the conflict and it remains that of political transition built on compromise, with a transitional government involving pragmatists from regime and non-regime camps. While the world is occupied with the immediate repercussions of the attack, the focus should be on what should happen in the long run, underlining the need to couple military action with political strategy.

There can never be peace in Syria while the regime of Bashar al-Assad is in power. As long as it is there, the original grievances that led people to protest against it will continue to exist, along with growing distress driven by the behaviour of the regime over the past seven years. The parameters of this behaviour are not going to change were the regime to “win”: as history has shown, dictators do not turn into reformists overnight.

Lina Khatib is head of the Middle East and North Africa Programme at Chatham House, where she leads the Syria from Within project