It was a dramatic reversal, not only from Trump’s own pledges to limit U.S. involvement in Syria but from his predecessor, who for years resisted growing calls to intervene militarily against the Assad regime. President Barack Obama’s decision to refrain from engagement in 2013 was criticized as feckless at the time and is cited now as one of the reasons that Trump was forced to act. But a revisiting of the arguments and calculations that led Obama to make his decision ― from the fear that it would not be a deterrent to the concerns over how the U.S. would respond to future attacks on civilians ― provides an important blueprint for the major hurdles that Trump will now have to confront.

Even if the Assad regime stops using chemical weapons, it will continue to pummel civilians with barrel bombs, predicted Ilan Goldenberg, a former State Department official during the Obama administration. “You’ll see many more pictures of ‘beautiful [Syrian] babies’ [dying] on TV ― specifically to humiliate the United States and show the fecklessness of military action,” he said.

“What will the United States do? Will it get drawn in the way it did in Libya where we started with a civilian protection operation and ended up with a regime change operation?” Goldenberg continued. “This is the biggest danger and I think this was Obama’s biggest concern.”

The Obama administration resisted getting pulled into the Syrian civil war, which began during the Arab Spring protests in 2011. But in August 2013, a sarin gas attack allegedly carried out by the Assad regime killed 1,400 Syrians. It was a humanitarian catastrophe and a clear challenge to Obama’s self-imposed “red line” against the use of chemical weapons, which he laid out the previous year. At first, Obama appeared poised to respond quickly with limited airstrikes ― a variation of what Trump did on Thursday. Three days after the 2013 chemical weapons attack, the U.S. sent armed warships into the eastern Mediterranean Sea and the military drew up attack plans.

But Obama never ordered the military to strike. In the days following the 2013 gas attack, the administration attempted to drum up international and domestic support for a retaliatory response. Obama had hoped for a coordinated response with an ally, but the British Parliament voted down the United Kingdom’s participation. Their vote raised the specter of whether Obama, as well, would allow his government’s legislative branch to have a say. After a 45-minute walk around the South Lawn of the White House with his chief-of-staff, he announced that he would ask for congressional approval ― even as he maintained that he had the authority to order the strike without consulting lawmakers.

By that point, however, it was becoming clearer that the American public, still reeling from drawn-out wars in Iraq and Afghanistan and an ill-fated intervention in Libya, opposed the move. Lawmakers said they were inundated with calls from constituents urging them to vote against military action. After weeks of deliberation, it was unclear if Obama could get enough votes from Congress. By the time all the views within the administration had filtered up to Obama, he had heard passionate cases both for and against intervention, said Perry Cammack, a staffer for then-Secretary of State John Kerry, at the time. And then, in what appeared to be an-off-the-cuff rhetorical remark, Kerry told reporters the only way for Assad to avoid military action was to turn over his chemical weapons stockpile to the international community within a week. “But he isn’t about to do it and it can’t be done,” Kerry said.

Russian Foreign Minister Sergey Lavrov jumped at the narrow opportunity. Five days later ― Washington and Moscow announced a deal in which Syria would do what Kerry had almost jokingly proposed. Obama called off the military strike.

Ruben Sprich/Reuters Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov in September 2013, after announcing an agreement aimed at eliminating the Assad regime's chemical weapons arsenal.

In the years since, even some of Obama’s most strident supporters questioned whether this was the right call. Backing down, they said, damaged U.S. credibility and strengthened Assad’s sense of impunity. But even as the civilian death toll in Syria mounted, Obama maintained that he’d acted prudently. A limited strike would have no practical effect on the Assad regime ― and surviving an attack from the U.S. risked emboldening rather than deterring the dictator, his camp argued. Obama also worried about starting down the slippery slope to deeper involvement in another quagmire in the Middle East.

Whereas Obama has been faulted for overthinking matters to the point of crippling inaction, critics of the current president say his weakness is his apparent lack of interest in planning. “I have no confidence these guys have any plan whatsoever,” Goldenberg said.

Moreover, all of the concerns that made the Obama administration second-guess military action in Syria are still relevant today. If anything, the situation there is messier now than in 2013. The Islamic State militant group controls parts of Syria and Iraq. The U.S. air war against the group depends, in large part on Syria staying out of the way. Meanwhile, Russia has entered the Syrian civil war as a staunch defender of the Assad regime, providing air support to the embattled dictator. The crowded airspace is managed by a fragile deconfliction pact between the U.S. and Russia.

Trump seemed to recognize these complications too ― both during the 2013 debate when he strongly advised the U.S. not to engage in Syria and the presidential campaign when he warned that involvement would precipitate World War III. But in a span of a news cycle, his tune changed this week. During his daily intelligence briefing on the day of the attack, he asked for military options, White House Press Secretary Sean Spicer told reporters. Two days later, he had settled on an option and ordered the military to move forward. His administration notified foreign allies and congressional leadership after the missiles were launched, minutes before they hit their targets.

The haste with which Trump acted stands in contrast to the weeks of deliberation culminating in a decision not to strike in 2013. Cammack, the former Kerry staffer, described it as “a reflection of the temperaments of the two presidents.”

But it also allowed Trump to avoid a pitfall that ensnared his predecessor. By moving swiftly, the president earned plaudits from lawmakers and pundits ― some of whom swooned over the images that the military had released of the damage to the Syrian airfield. Even those who have accused Trump of being unhinged in the past praised the strikes as a decisive and proportionate response to Assad’s use of chemical weapons. That might be because the U.S. was already regularly dropping bombs in Syria against ISIS, making the public somewhat desensitized to further military action there.

But it also could be because by skipping the deliberative process that the Obama administration so meticulously engaged in, the Trump administration didn’t give the public time to sour on the idea.

I’m worried about whether they did enough of their homework given how quickly decisions were made. Eric Pelofsky, former NSC official

And yet, the speed with which Trump flipped positions and ordered military action based on his newfound distaste for the Assad regime risks doing exactly what Obama feared in 2013: sparking a series of unforeseen consequences. It is unclear whether the strikes will have any meaningful impact on the Assad regime. Hours after the U.S. attack, Reuters reported that Syrian warplanes took off from the base hit by American cruise missiles. On Friday and Saturday, Khan Sheikhoun, the opposition-held site of the chemical weapons attack earlier in the week, was hit by more airstrikes.

“I’m worried about whether they did enough of their homework given how quickly decisions were made,” said Eric Pelofsky, a former National Security Council official in the Obama administration. “ What happens if the Assad regime targets our aircraft as they are continuing to prosecute the war on ISIS inside Syrian airspace? Are we prepared to take down their air defenses ― and for the consequences of doing that?” continued Pelofsky, who is now a fellow at the Washington Institute for Near East Policy.

Even some who criticized Obama’s inaction worried that Trump’s impulsive decision-making process could backfire. “Horrible as the Khan Sheikhoun attack was, the Assad government has used chemical weapons dozens and dozens of times, and has committed numerous other war crimes,” Kori Schake, a former Bush administration official, wrote Friday. “The indiscipline that has characterized the Trump’s actions may lead him to emotional reactions without corresponding strategy.”

S.V. Date contributed reporting.

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