Did you know Boris Johnson is British and American? Therefore if anything happened to him it would be considered not just an attack on a British prime minister but a British American prime minister. Would he also technically be allowed to run for president of the USA? He was born there.
He did say he wanted to be King of the World.
The tax thing is probably why there are not as many Americans as you would think there would be here teaching English. They have to get double taxed? That’s a serious disincentive to work abroad.