One of the worst things that Barack Obama did while in office was to announce a “red line” over the Syrian government’s use of chemical weapons and then, in 2013, refuse to enforce it. His failure to act gave Bashar Assad license to commit further atrocities, including the use of chemical weapons, as he did again this Tuesday. It also sent to the entire world a crippling message of American irresolution. Obama’s lack of credibility was obvious to predatory states such as Russia, China, Iran, and North Korea, and encouraged them to conduct further violations of international norms. It may not be entirely a coincidence that Vladimir Putin invaded Ukraine a year later; at the very least the U.S. failure in Syria must have reassured Putin that Obama would do little to stop him.

It is therefore of considerable importance that President Trump has now attacked a Syrian air base with 59 cruise missiles in retaliation for Assad’s use of chemical weapons. This is a small but significant step in regaining lost American credibility and putting America’s adversaries on notice. There is a new sheriff in town, and he will be far less hesitant than Obama was about the use of force.

Among other things, the strike signals to Vladimir Putin that, despite the undoubted help his intelligence services provided to Trump’s campaign by hacking Democratic emails, he cannot count on Trump to act in Russia’s interests, which in this case lie with supporting the Assad regime. The message for Iran is that the days of the U.S. ignoring Iranian-backed aggression against the Middle East are over—the new U.S. administration is no longer afraid to strike at Tehran’s number one proxy, the Assad regime, for fear of scuttling the nuclear deal.

This is all to the good, but it is unclear what Tuesday night’s strike means for the future of U.S. policy in Syria. After all, exactly a week before the cruise-missile attack, Secretary of State Rex Tillerson had said, “I think the… longer term status of president Assad will be decided by the Syrian people.” This was widely seen as an endorsement of the Assad regime, and one that may well have given Assad the confidence to use chemical weapons, secure in the (mistaken) belief that the U.S. would not respond.

And now? Tillerson says “it would seem there would be no role for [Assad] to govern the Syrian people.” But he also says: “I 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. There has been no change in that status.”

So does the U.S. now favor action to remove Assad from power or not? It’s unclear. Just as it’s unclear what, if anything, the U.S. will do in the future when Assad attacks civilians with conventional weapons, the kind that have caused the vast majority of the nearly 500,000 deaths in Syria’s six-year-old civil war.

The messages sent by the administration to explain the cruise missile strike focus not on the need to save Syrian lives, per se, or to bring Assad’s killing to an end but rather, more narrowly, on the need to reassert an international norm against the use of chemical weapons. As President Trump himself said on Thursday night, “It is in this vital, national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.”

This is a perfectly legitimate, if limited, step to take, but it would be greatly helpful to the entire world if Trump were to more fully explain why he acted and what the ramifications will be for U.S. policy. This is, after all, a head-snapping change of direction for a president who opposed the use of force in 2013 to enforce Obama’s “red line,” promised to stay out of the Syria “quagmire,” and said that his policy in Syria would be limited to working with Russia against ISIS. A president is free, of course, to adopt different policies in office from those he advocated on the campaign trail and many have. But it is incumbent on Trump now to explain why he has changed his mind and what this portends for future U.S. policy not only in Syria but elsewhere in the world.

Trump’s horror at the attack was real and affecting—“It was a slow and brutal death for so many, even beautiful babies were cruelly murdered in this very barbaric attack,” he said on Thursday night. “No child of God should ever suffer such horror.” But this was neither the first nor the worst such attack. Why did this one lead him to act after previously opposing action? The obvious explanation is that this one occurred on Trump’s watch and he was moved to respond by the horrifying pictures he saw on TV. But is he now setting a new standard for humanitarian intervention by the U.S. in response to gross human-rights abuses, or was this a one-time-only event?

The problem with Obama was that he was so deliberative and hesitant that he was often paralyzed into inaction. The danger with Trump is that he will be so impetuous and erratic that he will change course and lash out without thinking through the consequences. Thursday night’s strike was quite restrained, but, given how far removed it is from the kind of quasi-isolationist, “America First” foreign policy that Trump campaigned on, it does raise questions about where his administration is headed that the president would be well advised to address in a major speech laying out his evolving foreign-policy doctrine.