President Trump soured on Mike Waltz as his national security adviser for multiple reasons. But ultimately it came down to vibes when he replaced Waltz with Secretary of State Marco Rubio, who'll temporarily do both jobs.

Why it matters: The boot for Waltz — two days after the media circus on Day 100 — was this term's first big shakeup. It showed how responsive Trump remains to optics, even while feeling as empowered as ever.

How it happened: In Trump's mind, Signalgate was the first time he was unable to control the narrative or win the day, top advisers tell Axios.

• Waltz came to symbolize Trump's first obstacle. Momentum is so important to the president that he emphasized the concept in his advice last night to University of Alabama graduates.