President Donald Trump wants to punish Syrian strongman Bashar al-Assad for using chemical weapons against his own people last week. The question is when, or if, Trump will actually give the order — and whether such a strike will be enough to prevent Damascus from using nerve agents in the future.

Trump is considering the strike because of an April 7 chemical attack in Douma, a suburb of the capital, that killed more than 40 people. Syria has denied responsibility, but on Thursday, NBC News reported that the US now has blood and urine samples that indicate exposure to a chemical weapon.

In the immediate aftermath of the attack, Trump said he would exact a “big price” on Assad. But five days after the Douma attack, there’s more confusion than ever about what Trump wants to do.

On Wednesday, Trump tweeted that Russia should “Get ready” because missiles “will be coming” toward Syria. That afternoon, White House press secretary Sarah Huckabee Sanders told reporters that “all options are on the table” when it came to Syria, which suggested that Trump hadn’t actually decided to use force. And on Thursday morning, Trump tweeted he “Never said when an attack on Syria would take place.”

Now it seems like the question of a US strike is one of if, not when. Trump has yet to decide if he will authorize an assault on Syria, although he told reporters on Thursday that decisions will be “made fairly soon.” He’s also waiting to see if the UK and France will take part in any strike.

The problem is the more the US and its allies wait, the more time Syria and Russia — which helps support the Assad regime with warplanes and ground troops — have to prepare for an attack. And should an attack happen, there’s a small but real chance a shooting war with Russia becomes a possibility — especially if the US kills Russian troops.

But that’s not all: Assad has used chemical weapons in attacks on Syrians since 2012, and it’s unclear that a US-led punitive strike will take away the regime’s ability to keep using them. “It’s always very difficult to degrade these types of capabilities using airstrikes,” Rebecca Hersman, a former top Pentagon official on weapons of mass destruction (WMD), told me. “It tends to be a temporary process.”

In effect, striking Syria may seem like the right thing to do, but its effect may be limited.

“That’s a lot of attacks to ignore”

It’s worth stepping back to understand why Assad has used chemical weapons so often — and why he’s likely to continue doing so in the future.

Assad’s forces launched around 200 chemical attacks since the start of the war, Hersman told me, with mostly no response from the US. But when the US did respond — like when Trump had the Pentagon launch 59 Tomahawk missiles at Syria last April after an earlier chemical weapons attack — Assad went on to conduct over 20 more chemical attacks.

“That’s a lot of attacks to ignore,” says Hersman, who is now at the Center for Strategic and International Studies think tank in Washington.

This is why some experts believe the US should strike Syria soon, prompted by the attack in Douma last Saturday. “This is about holding Assad accountable for crimes against humanity,” Andy Weber, also a former top WMD official at the Pentagon, told me. “Assad has been able to conduct multiple attacks unpunished.”

But if Trump does decide to strike Assad, the operation won’t be so easy — and it could cause even more problems.

Hitting Syria won’t be easy

The US has the world’s strongest military, but it might face some challenges as it tries to seriously punish Assad for the chemical weapons attack.

Syria has already moved some of its aircraft to protect them from possible strikes. Some US officials told Reuters on Wednesday that Assad’s forces could put Syrian planes near Russian military positions to deter the US from ordering a strike that could hit Russian forces. Killing Russian troops — or even destroying Moscow’s planes — could escalate the already rising tensions between the White House and the Kremlin.

Syria also has an advanced missile defense system that could potentially down missiles shot by Western fighter jets or ships. Right now the US has two missile-carrying destroyers in position to attack Syria, along with warplanes and submarines. Britain, meanwhile, could direct its fighter jets and refueling aircraft currently engaged in the nearby anti-ISIS mission.

Moscow, expectedly, could help Assad defend his forces from the US and its allies. Russian Ambassador to Lebanon Alexander Zasypkin said Tuesday that the Russian military could shoot down any missiles the US launched at Syria, adding that Russia could shoot back at American planes or ships. Russia has stationed some of its most powerful warplanes in Syria, which Moscow may mobilize to impede any US-led campaign to bomb the Assad regime.

Let’s say, though, that the US manages to destroy the helicopters the regime uses to drop chemical weapons without killing any Russians. What then?

Sadly, it’s unlikely that Assad will stop using chemical weapons. He knows he can get away with other, smaller attacks once Trump and Western leaders focus their attention elsewhere. That’s why Hersman and Weber believe the West needs to respond more aggressively, and with more tools, the next time Assad uses chemical weapons.

“A one-time attack may not achieve all of our objectives,” he told me.

In practice, that means the US and its friends should always respond to a chemical attack in Syria with a combination of military, diplomatic, and economic moves. Options for those responses include strikes, if necessary, but also sanctioning the regime or diplomatically ostracizing countries that support it, especially Russia and Iran. Assad, in theory, would then increasingly realize he will face a penalty every time his forces use chemical weapons.

At this point, though, it doesn’t seem like Trump is willing to go further than a limited missile strike. And that means Trump is pretty much guaranteed to face another moment like this, and probably sooner rather than later.