As an NBC News reporter covering former President Donald Trump, I’ve attended more than a dozen of his campaign rallies this election cycle alone. They usually feel more like concerts or festivals than political events, with food trucks and vendors, where supporters and their families gather to enjoy the day.

That’s how Saturday’s rally in Butler, Pennsylvania, started, too. But, as we all know, that’s not how it ended.

A few minutes into Trump’s speech, my producer, Bianca Seward,…