[Errant]

It's moving much too slow to be a missile IMO. Most likely a contrail from an aircraft at a very high altitude.

There's lots of important issues to be concerned about. This isn't one of them but it is a sign of how jumpy everyone is.

[Errant]

Even a BROKEN Trident travels much faster:

Trident II launch goes wrong

[BradyLS]

I saw the video. I know what jet contrails look like. Way too much plume going vertical to be a jet contrail. That was a rocket or missile of some type. An SLBM, by the looks of it, launched just over the horizon. And footage of one of those isn’t hard to find to compare them.