Look, it had just started to rain when Trump began the speak, they were passing out ponchos and having umbrellas ready for dignitaries Then the rain slacked up and they left. That is all
I liked the 'they were there to protect Trump from a shiv wielding Hillary' theory. Your explanation is more boring. And most likely correct.
There were some individuals who passed out umbrellas. But this group from different services marched out in formation, stood at attention for several minutes, and then marched off. I didn’t see them passing out anything. It was very unusual.