Assassinating someone on Russian soil is a great way to start a war. You seem to be assuming that it could be covered up successfully. History proves otherwis

Assassinating someone on Russian soil is a great way to start a war. You seem to be assuming that it could be covered up successfully. History proves otherwise; all too often, the truth comes out eventually. And if he were assassinated, the party responsible would be fairly obvious early on, because there's only one country that would have the motivation to finance that operation. Putin gives him protection because it lets him thumb his nose at the US.