President Trump just threatened to bomb “Gas Killing Animal” Bashar al-Assad’s government in Syria just a week after publicly musing about withdrawing US troops from the country. Trump taunted Russia and dared the Kremlin to try to shoot down American missiles — and then sent another tweet saying he wants to improve US-Russia relations.

This seeming incoherence when it comes to major foreign policy decisions is a hallmark of the Trump presidency so far.

Trump says he wants to buddy up to Russia and then expels 60 Russian diplomats; he swings from publicly dismissing the idea of negotiations with North Korea to agreeing to sit down with its supreme leader; he slaps huge new tariffs on China and then talks about how friendly he is with Chinese President Xi Jinping.

On issue after issue, the president’s statements contradict his aides’ comments, his administration’s actual policy, and even his own past statements. Contradiction itself feels less like an error and more like the only real Trump doctrine.

This is not a good thing for US foreign policy — or the world.

“Emotionally, it’s incredibly dispiriting to see matters of life and death tossed around so lightly,” says Paul Musgrave, a scholar of US foreign policy at the University of Massachusetts Amherst. “Analytically, it’s horrifying to see a president whose policymaking agenda is set so trivially.”

The serious problem with Trump’s Syria-Russia tweets

Part of this is because the president doesn’t have many strong or fixed policy preferences and is often guided by his emotions or what he sees on TV.

He decided to bomb Assad’s government for the first time last year, according to White House insiders, because his daughter prepared a slideshow with images of children poisoned by Assad’s chemical weapons. This came after years of railing against the idea of US intervention against Assad — at one point during the campaign, he even suggested he might consider partnering with the Syrian regime to fight ISIS.

The ping-ponging of presidential feelings makes it extremely difficult for the administration to craft a consistent message or policy. What’s more, Trump’s unfiltered use of Twitter — on display Wednesday morning — makes it easy for him to change things on a dime.

The problem with this is that functioning foreign policy depends on being able to send messages about what you’re planning to do. When the US threatens to use military force against an adversary, that’s a commitment about what the country will do in the future. The policy only works if people think you mean what you say.

Imagine all the ways this could go wrong when it comes to Syria, for example. What if the seemingly inevitable US strike hits Russian or Iranian troops who are on the ground fighting for Assad? What if an American warplane gets shot down by Syrian air defenses?

In the event of such a crisis, the signals sent from Washington will be critical to prevent the situation from escalating dangerously. But which words will foreign leaders take seriously? How will they know what the United States will actually do next, and what they need to do to avoid provoking another response from the US military?

“If we’re having trouble [interpreting Trump] in the US, imagine what it’s like being in a foreign capital,” says Dan Nexon, a professor at Georgetown University. “Especially if you’re somewhere that already has trouble understanding US foreign policy and political processes.”

The fact that this happens so frequently, on so many different foreign policy issues, means that American foreign policy in general is less likely to function as desired. Trump has regularly questioned the value of NATO, for example, but also said he’s willing to defend NATO allies in the event of an attack. How seriously should Russia take the latter pledge in light of the former comments?

The honest answer is we aren’t sure. And this policy of incoherence, especially incoherence set off by tweet, could lead to a very serious mess — in Syria or elsewhere.

“By sending out such a high volume of cheap talk, he’s increasing the chances of terrible miscalculation,” Musgrave says. “What if the tweet about smart bombs had been directed at North Korea?”