Large unusual motorcade - who for?

Was just getting on 395 N near the Pentagon (toward DC) and saw the largest, most unusual motorcade I’ve ever seen.

Entrance ramps and over passes blocked, lots of police car and motorcycles, a lot of coach buses — maybe 8 of them? The first several were full but the last few were empty, then 2 smaller buses, like you sometimes see for press? (Also empty)

But the kicker at the end was an ambulance (weirdly from Silver Spring?).