During his hotly anticipated speech in Saudi Arabia on Sunday, President Trump made a big pivot on his relationship with the Muslim world. He dropped the use of the term “radical Islamic terrorism,” the inflammatory phrase he frequently criticized Barack Obama and Hillary Clinton for being unwilling to say.

Instead, he chose to go with a less antagonistic phrase: “Islamist extremism.”

Or, well, he was supposed to.

According to his prepared remarks, he was supposed to use the terms “Islamist extremism” and “Islamist terror” in his speech. Instead, as reporters noticed, he used the term “Islamic extremism” and “Islamic terror.”

Those terms might seem similar, but there’s a significant difference between them — and it’s big enough that a senior White House official tried to justify the slip-up by saying the president tripped up because he was “exhausted.”

The term Trump used, “Islamic,” means anything having to do with the religion of Islam. The term he was supposed to use, “Islamist,” refers to matters relating to the political project of reorganizing the state and society in accordance with the laws of Islam that can be deduced from Islamic texts. Put another way, “Islamic” is a bigger umbrella that signifies anything tied to the religion, while “Islamist” is a smaller umbrella that covers issues tied to political Islam.

So why does this matter?

By using the term “Islamist extremism,” the Trump White House is implicitly acknowledging that there is such thing as moderate Islamism, which is a real phenomenon.

Consider, for example, the largest political party in Tunisia, Ennahda. It was inspired by Egypt’s Islamist Muslim Brotherhood, but it’s a moderate party that’s grown far more secular in recent years and is known for being a compromiser in Tunisian political life. Its ideology shouldn’t be placed in the same category as, say, ISIS’s ambition to conquer the world and subject it to a harsh, militant interpretation of Islamic law.

More importantly, the term “Islamist extremism” is also slightly further away from a description of Islam as the problem. For some English-speaking Muslims, fighting Islamist extremism sounds more nuanced and targeted than Islamic extremism, and takes the fight slightly further away from the cultural sphere. It’s a term that stands more in accordance with Trump’s new position that his anti-terror campaign “is not a battle between different faiths, different sects, or different civilizations.”

Whether a militant group that carried out terrorist violence identifies itself as Islamist or Islamic doesn’t really matter that much. But Muslims in the US and around the world look at Trump as the most Islamophobic figure in American political life in recent memory, and watch his words closely — the nuances matter. The absence of the word “Islamic” would be a more concrete, even if modest, sign of progress.

It’s possible this is the first and last time Trump will make this slip-up, and that it was indeed a product of fatigue. (That should in and of itself be a source of huge embarrassment for Trump, who places great value on “stamina” and enjoys vanquishing “low-energy” rivals.)

But a more plausible explanation is that he doesn’t understand the difference between the two terms and glossed over the word while reading it off a teleprompter without realizing it. That makes it seem more likely that he’ll slip up again in the future, whether during meetings or at future speaking events, and continue to cause confusion by breaking from his administration’s formal stance on the matter.

Some would call the Islamic-Islamist point a distinction without a difference. During his presidency, Barack Obama was opposed to using either variation — radical Islamic or radical Islamist — because he felt that invoking the religion’s name at all was a smear to Islam and alienated Muslims across the globe.

George W. Bush consistently referred to Islam as a religion of peace and framed his counterterrorism agenda as a “war on terror.” Whether Trump uses the old term, radical Islamic terrorism or the new term, Islamist extremism, he’s still putting Islam front and center compared with his predecessors.

Ultimately, at the end of the day, his deeds will likely resonate more than his words. His repeated attempts to stanch the flow of travelers from Muslim-majority countries will likely ring louder than any subtle shifts in rhetoric.