President Donald Trump decided to strike Syria on Friday night, and he might incur some unintended consequences — like increasing the risk of getting into a shooting war with Russia.

On Tuesday night, Russia’s ambassador to Lebanon said the Russian military could shoot down any missiles launched at Syria, and even retaliate against the planes or ships that fire the weapons. (As of now, there is no indication that any Americans were hurt in the strike.) But Trump responded to the threat the following morning, egging Russia on with his characteristic bravado.

“Get ready Russia, because they will be coming, nice and new and ‘smart!’” Trump tweeted on Wednesday. “You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!” he added, in reference to Syrian President Bashar al-Assad.

That exchange came as Trump weighed how to punish Damascus after Assad’s forces carried out a suspected chemical attack on civilians on April 7, killing at least 40 people. Trump promised a big response and has consulted with his national security team and foreign leaders for days about whether, and how hard, to strike the Syrian government.

Here’s where things get complicated: Russia is a staunch Assad supporter and has helped prop up the regime since Russia’s September 2015 intervention in the civil war. Russian warplanes drop bombs in Syria, helping Assad kill hundreds of thousands of anti- government fighters and civilians. Moscow also has Kremlin-linked troops, which it labels as mercenaries, in the country to help fight anti-Assad forces. Some of the mercenaries even attacked American troops.

Trump has repeatedly expressed his desire to improve relations with Russia. But experts tell me there is a chance of a broader US-Russia fight if the strikes go awry.

“The risk is there, but I think it’s small,” Bilal Saab, a defense expert at the Middle East Institute, told me before the Friday night attack by the US, France, and Britain. “But if we kill, deliberately or accidentally, Russian soldiers, there’s a real chance Russia could launch, directly or by proxy, attacks against our troops in Syria.”

That, in the grand scheme of things, is the issue. Russia might look away if American strikes only punish the Syrian government in a relatively limited way. But if the US strikes Russian assets — especially its military personnel — then things could move in a different direction.

“We could stumble into direct conflict very quickly,” says Heather Conley, a European security expert at the Center for Strategic and International Studies think tank. “The nation is not prepared for this eventuality.”

Both Russia and the US seem to want to avoid an escalation — for now

Washington and Moscow have had some close calls in Syria, but so far they have avoided a serious altercation.

Almost exactly one year ago, Trump launched a military strike on Syria in response to an Assad-ordered chemical weapons attack in rebel-held northern Syria. The United States shot 59 Tomahawk missiles at the al-Shayrat airbase, where Assad had launched the chemical attack on April 4, 2017, that killed more than 80 people. The strikes provoked no significant Russian reaction.

Last June, the US shot down a Syrian warplane. It was the fourth time in a month that the US struck pro-Assad forces, and the first time the US brought down a Syrian military plane since the war’s start. In the aftermath of the incident, Moscow said it would “target” US-led coalition aircraft flying above Syria. It even cut off contact with the US, which was bad news, since Washington and Moscow were in close contact to ensure they wouldn’t get into a military confrontation. That contact has now been restored.

Despite those two incidents, America and Russia didn’t come to blows. But those flare-ups paled in comparison to a very scary — and deadly — firefight this year.

On February 7, Russian mercenaries fired at American troops in eastern Syria. It was the first time in 50 years that US and Russian troops directly fought one another. (America’s 2,000 troops are in the country to fight ISIS; Russian troops are there to help Assad.)

The US repelled the attack, killing around 200 to 300 Russian mercenaries and other pro-government fighters. There were no US casualties. Brig. Gen. Jonathan Braga, who helps lead anti-ISIS operations, told NBC News on March 15 that he was “absolutely concerned” the event could lead to a greater US-Russia fight.

But tensions soon died down. “Russia and the US were able to iron out the dispute,” says Shanna Kirschner, a Syria expert at Allegheny College, “which strongly suggests neither side wanted to escalate at that time.”

“But it’s not a given that continued casualties wouldn’t be a provocation,” she added.

That’s perhaps why Trump may use “smart bombs” to attack Syria, which he alluded to in his Wednesday morning tweet. Smart bombs, typically, can evade missile-defense systems and then precisely hit the target. They can help minimize any unintended casualties, like killing Russian soldiers, if they are near the target the US wants to strike.

Experts believed the US will work with Russia to avoid that outcome. “I suspect that we’ll be communicating with them,” Faysal Itani, a Syria expert at the Atlantic Council think tank, told me before the strikes.

There’s also a political element to this. Trump wants closer ties with Moscow, and even tweeted on Wednesday — right after his missile attack threat — about why the US and Russia should work more in tandem. It’s therefore hard to believe he would imperil the US-Russia relationship by targeting Russian troops during Syria strikes.

Our relationship with Russia is worse now than it has ever been, and that includes the Cold War. There is no reason for this. Russia needs us to help with their economy, something that would be very easy to do, and we need all nations to work together. Stop the arms race? — Donald J. Trump (@realDonaldTrump) April 11, 2018

Russian President Vladimir Putin may not be as concerned with improving Moscow’s relations with Washington, but he also doesn’t want a war, says Kirschner. Plus, starting that fight would suck time and attention away from Putin’s effort to help Assad, and his ongoing war in Ukraine.

The question is, can the US and Russia avoid getting into a broader fight after the US launches missiles at Syria, even if neither side wants this? Fred Hof, President Obama’s special adviser for transition in Syria, told me that “nothing is risk-free.”

“I suspect neither side wants a direct confrontation,” he continued, “but when things go flash-bang, there are always surprises and unintended consequences.”