The timing of Syrian President Bashar Assad’s chemical attack on his own people probably wasn’t an accident.

Assad’s military launched its brutal attack on civilians – using substances he had vowed to get rid of under a deal struck with Russia and the Obama administration in 2013 – mere months after US President Donald Trump took office.

Now Trump has sent a signal that Assad’s actions won’t go unpunished.

On Thursday night, the US launched a salvo of 59 cruise missiles on Shayrat airfield and nearby Syrian military infrastructure in response to the chemical attack that killed at least 80 people in the northwestern part of the country on Tuesday.

Steven Cook, a senior fellow at the Council on Foreign Relations, said Assad’s latest attack seemed to be a test of how the new US president would react.

Assad's father, the former president of Syria, "mastered this way of testing his enemies and doing just enough to keep enemies at bay while retaining the options to continue to do bad things," Cook told Business Insider.

"That's clearly what Assad did with chemical weapons."

Cook explained that as the new administration in the US seemed to signal a change in policy - on the campaign trail, Trump talked about closing US borders to Syrian refugees - Assad might have decided to see what he could get away with.

"For the life of me, I can't understand the strategic value of using the chemical weapons in this town," Cook said. "It seemed to be a way to see how the Trump administration is going to respond."

It remains to be seen whether this strike against Assad's military represents a major shift in US policy toward Syria. Secretary of State Rex Tillerson said Thursday that he "would not in any way attempt to extrapolate that to a change in our policy or posture relative to our military activities in Syria today."

Fred Hof, the director of the Atlantic Council's Rafik Hariri Center for the Middle East and former US special adviser on Syria, told Business Insider that the strike would "either be a one-time, one-off, fire-and-forget retaliation for a heinous chemical weapons assault on civilians, or it will serve as a signal to the Assad regime and its allies that the free ride for mass murder in Syria is now over."

Assad's atrocities against civilians aren't new. He has for years used everything but nerve gas - including chemical weapons like chlorine - to bomb schools, marketplaces, and hospitals. The attacks have been well-documented but have not inspired international action.

"Assad struck with chemicals because his sense of impunity had over years of Western apathy and inaction become absolute," Hof said.

The Obama administration never directly struck the Assad regime.

President Barack Obama in 2012 drew a "red line," threatening military action if the Assad regime used chemical weapons. Once evidence surfaced of such an attack in 2013, Obama backed off his threat of military force and instead opted to cut a deal in which Assad agreed to remove his stockpile of chemical weapons, including the nerve agent his forces are thought to have used this week.

Some experts have argued that this inaction from the US had emboldened the Assad regime.

With the latest attack, "perhaps [Assad] wished to demonstrate to his opponents that further resistance was useless, that the world would do nothing in response," Hof said. "Clearly, he miscalculated."

Still, if Assad continues his attacks on civilians using other weapons and the US does nothing, the US strike "will go down in history as a useless, empty gesture," Hof said.

It's likely that the Trump administration will be tested again in the future.

After the US strike, the Syrian army accused the US of "blatant aggression" and said it would respond by continuing to "crush terrorism." The Assad regime considers any opposition forces, including the rebels who are trying to remove him from power, to be terrorists. The regime also has not distinguished civilians from combatants in the past.

"If the strikes of April 6, 2017, end the Assad crime wave against Syrian civilians, good," Hof said. "If they do not, further action will be essential."