We’ve already seen signs of mission creep in Syria. This week, the Trump administration completely reversed its position on Assad’s political future. Having stated that removing Assad was no longer a priority, the administration then announced that there was no place for the dictator in Syria’s future, and “steps are underway” to remove him. After the air strikes, U.S. Ambassador to the United Nations Nikki Haley said the United States was “prepared to do more.” Russia announced that relations with the United States were “completely ruined.” Hawkish senators like John McCain and Lindsey Graham urged a broader mission to ground Assad’s entire air force.

Wars have a habit of evolving in unexpected ways due to a combination of psychology, domestic political pressures, and strategic interactions. Psychologists have found that the act of committing to a decision—like launching air strikes against Syria—can make decision-makers overconfident that they made the right choice. A classic study from the 1960s showed that after people made a bet at a racetrack they immediately became more confident their horse would win. Psychologists Heinz Heckhausen and Peter Gollwitzer later developed this idea into the “Rubicon Model of Action Phases,” named after Caesar’s fateful choice in 49 BCE. When people first weigh up different options, they are fairly objective and clear-headed. But after making a decision, they become zealots of their chosen course of action—and suddenly wildly optimistic it will succeed. As Gollwitzer put it: “Choosing between action goals leads to realism; and implementing chosen goals leads to positive illusions.” After Trump crossed the Rubicon, any doubts he had may have been replaced by confidence—the kind of mindset that could easily broaden the war.

Another escalatory dynamic comes from how the operation is framed. Leaders sell military campaigns to the American people using highly moralistic language. But this makes it difficult to end the war with anything less than regime change. Trump described the chemical weapons attacks as “a disgrace to humanity” and said, “no child of God should ever suffer such horror.” If Assad is so evil that the United States must use force, how can America let this devil stay in power?

And, of course, the other guy gets a vote, which can dramatically shape the course of the fighting. Assad, or one of his allies like Hezbollah or Iran, might conceivably retaliate against the United States or Israel, essentially forcing the White House into further escalation. More likely, however, is that Assad will respond by pushing boundaries and then claiming victory. Limited air strikes rarely cause regimes to significantly alter their behavior for one simple reason—the regime doesn’t want to look weak, either at home or abroad. Assad is engaged in an existential fight. His country is in ruins. Half the population is displaced. He’s not going to bend to America’s will because of a few craters on an airfield. Instead, Assad will probably respond by avoiding an explicit repeat of the sarin gas attack, and returning to tried and tested techniques like systematic torture, barrel bombs, chlorine weapons, or the real weapon of mass destruction, shelling—all the while boasting about his defiance of America.