During last year’s presidential campaign, Donald Trump and Hillary Clinton had heated debates over Syria. Clinton took a hardline stance, advocating more airstrikes against the Islamic State and the enforcement of no-fly zones, even at the risk of clashing with President Bashar al-Assad’s ally in the conflict, Russia. Trump countered by arguing that if defeating ISIS was so important, the United States should be willing to work with anyone. “I don’t like Assad at all, but Assad is killing ISIS,” Trump said during his second debate with Clinton. “Russia is killing ISIS. And Iran is killing ISIS.... I think you have to knock out ISIS.”

Trump was, in effect, calling for a grand alliance against the Islamic State, but it’s become abundantly clear that this is not to be. Instead, the president is undergoing a remarkable transformation on Syria: He’s rapidly turning into Hillary Clinton, and it’s making a major U.S. war more likely.

Though Trump derided such an approach in debates with Clinton, the U.S. is now fighting a multi-pronged war in Syria, as opposed to focusing exclusively on ISIS. In April, after a chemical weapons attack by Assad forces, Trump ordered a missile strike on a military airfield—a harbinger of a shift in policy, it now seems. Over the past week, the U.S. has downed two Iranian-built drones, and on Sunday the military shot down a Syrian jet—the first time the U.S. has done so in this war. In response, the Russian government suspended its air-traffic hotline with the U.S. and warned that it might target U.S. and allied planes if they fly west of the Euphrates.

The U.S. now finds itself in a much more dangerous situation in the Middle East, where the war against ISIS, which has broad bipartisan support, could become a wider regional conflict of the type that Trump specifically promised to avoid.

This shift is partially a response to success on the field. ISIS is in retreat, and expected to lose its strongholds in Mosul (in Iraq) and Raqqa (in Syria). Thus, the various factions fighting ISIS have no reason to form the alliance that Trump hinted at. Instead, they are already preparing for a post-ISIS world by securing as much territory as they can. For Iran in particular, the end of ISIS would be their biggest unexpected bounty since the early days of the George W. Bush administration, when the U.S. obligingly removed Saddam Hussein and the Taliban from power in Iraq and Afghanistan, respectively. With ISIS out of the picture, Iran would have an unbroken swath of allies from Iraq to Syria to Lebanon—a land bridge to Israel’s border.

“As ISIS disappears off the map,” Ilan Goldenberg, a former state department official, told to the Guardian, “this tolerance that Shia Iranian-supported groups and American-supported groups have shown for each other—there is a danger that will go away. You can see it all going haywire pretty quickly.”

Goldenberg’s warning should be heeded. Clinton’s policies were controversial but at least sprang from a coherent foreign policy worldview which could be debated. Trump might be following Clinton’s policies in broad outline but with little thought to consequences. He appears to be responding to unfolding events in an ad-hoc way, rather than being guided by a broader strategy. This “incremental escalation,” according to national security expert and former Obama adviser Colin Kahl, could quickly escalate because of the “asymmetry of stakes.”

Kahl notes that despite Trump’s more aggressive stance in Syria, the Assad regime, Russia, and Iran “haven’t backed down. They keep pushing, probing, testing, countering. They haven’t been cowed & deterred.” That’s because, whereas “the interests for the U.S. are important,” they are “vital” for the “Axis of Assad.” For Iran, the conflict is a chance to prop up a key ally in its broader regional struggle against Saudi Arabia. For Russia, propping up Assad would be a victory for their policy of national sovereignty versus America’s preference for regime change. For Assad, as Kahl says, the interests are “existential”—and not just for his government. If his regime falls, he may well end up like Hussein.

So the “Axis of Assad” won’t back down. Will Trump? Kahl seems pessimistic. If the axis retaliates over these recent provocations, the hawks in Trump’s National Security Council “will argue U.S. credibility has now been engaged, so we have to keep punching.” In effect, Trump is playing a game of chicken with foes that cannot afford to surrender, and the president might refuse to back down out of fear of losing face.

The pressure on Trump to escalate will come from outside his administration, too. Trump has made its alliance with Saudi Arabia the cornerstone of his Middle East foreign policy, which means supporting the Saudi government’s view of Iran as the chief promoter of instability and terrorism in the region. Saudi Arabia would welcome America joining in its larger regional proxy war against Iran.

In Congress, Iran hawks will welcome Trump’s shift on Syria. Because the president is a foreign policy novice with heterodox views, Congress has been unusually eager to serve as backseat drivers for his diplomatic efforts. On Iran, there’s a strong contingent of Republicans and Democrats who think Trump is not hawkish enough. House Intelligence Committee chairman Devin Nunes, known for his protectiveness of Trump in the Russia investigation, told the Washington Examiner, “One of my highest concerns is the Iranians’ ability to get a land bridge out to the Mediterranean to increase their logistical support for terrorist networks.” New York Congressman Eliot Engel, a member of the foreign affairs committee, said he worries that “there will be some collusion between Russia and Iran.”

A final factor that makes escalation likely is that the State Department, which normally would establish a modus vivendi for the post-ISIS Middle East, is being gutted by the Trump administration. With the department understaffed and demoralized, and managed by a secretary who seems isolated from the agency he oversees, America’s Middle East policy won’t be guided by those who believe in diplomacy. Trump’s preference for bilateral, zero-sum deals is at odds with the balance-of-power approach needed with divergent parties like Syria, Saudi Arabia, Iran, and Russia. This would be a monumental challenge for even the most skilled diplomat. Under Trump, it looks impossible.

The good news is that with ISIS on the decline, the type of nihilistic violence it sponsored might also diminish. The bad news is that the broader regional problems that created ISIS—sectarian strife, failures of governance, and despair over the permanent rule of autocrats—remain unchanged, if not worse. Indeed, if the U.S. continues to escalate this proxy war in Syria, these problems will only spread. “Red alert” indeed, and may cooler heads prevail somewhere within Trump’s hot White House.