I have an idea of the [19] who would cease to exist if POTUS, et al are harmed.

This is a real long shot but QE2 and her line of succession to the throne includes 18 people. Although he is not in line for the throne it seems prudent to include Prince Phillip in this list, which makes 19 people.

I've always assumed (bad idea when dealing with Q) that the [19]'s are all the same people but this seems intriguing.