I get why you might think that, but that same argument can be made about the missiles Ukraine has been shooting into Russia that were provided by the US. They’re perfectly capable of carrying a nuke, and Russia would have no way to know until it hits. So from Russia’s perspective we are already in the realm of playing with MAD. They have no reason not to do the same thing.
Also edit to add even IF it was confirmed to be a nuke Russa was launching if they target somewhere like Poland for example it’s very unlikely the US would launch their own nukes in that case. They’re not gonna risk the US mainland to save Poland. So when it comes to hitting non-nuclear NATO nations with ICBMs using conventional payloads its really just up to Russia if they want to try. MAD doesn’t work at all in that case.
I get why you might think that, but that same argument can be made about the missiles Ukraine has been shooting into Russia that were provided by the US. They’re perfectly capable of carrying a nuke, and Russia would have no way to know until it hits. So from Russia’s perspective we are already in the realm of playing with MAD. They have no reason not to do the same thing.
Also edit to add even IF it was confirmed to be a nuke Russa was launching if they target somewhere like Poland for example it’s very unlikely the US would launch their own nukes in that case. They’re not gonna risk the US mainland to save Poland. So when it comes to hitting non-nuclear NATO nations with ICBMs using conventional payloads its really just up to Russia if they want to try. MAD doesn’t work at all in that case.