Nasty wreck on video with a trailer being towed!

This one appears to have begun with a little help from a passing SUV. He wasn't speeding, doesn't appear to be windy, road looks normal, no evasive maneuver, just oscillation that continued to get worse. I'd bet lunch the owner lightened tongue weight to accommodate the Expedition. Doesn't make him evil, stupid or careless. He may have been ignorant of how little it takes off the tongue to induce sway.

https://www.youtube.com/watch?v=miE3MOcqn7E