Really really really broad brush answer = don't sweat it from anyone that has 'em right now and for the foreseeable future.
ICBM's = nuclear delivery.
Nuclear delivery = poison the earth/water.
Refer to a map of the USA. & a map of where our silos are.
The "breadbasket" & the Great Lakes combine to keep the USA safe from a nuke attack via ICBM.
In the global scheme of things, the food potential and the supply of potable water prevents anyone with any brains from risking poisoning it for a thousand years or more.
The irony here is that the more work we (the USA) do to help establish sources of food and clean water around the globe, the more we increase our own risk.
