This really has nothing to do with the altitude of the missile. Any ICBM that the US sends over Russia without talking with them first would be an extreme prov

This really has nothing to do with the altitude of the missile. Any ICBM that the US sends over Russia without talking with them first would be an extreme provocation, and would give Russia justification to do whatever they wanted (hopefully WWIII wouldn't result, but lots of other bad things could happen). This is not the same scale as North Korea test firing a missile over Japan (and look how nervous Japan got). Pre-coordinating a strike with Russia removes the time advantage that ICBMs have over bombers, and it would be a rare situation where Russia would give permission to let an American nuke overfly its territory. Similarly, if Russia shot an ICBM over US territory at any altitude, the US would freak out and be justified in sanctioning the crap out of Russia. Unfortunately, the US is not in the way of any of Russia's targets (unless the target is the US), so it's mostly a one-way consideration.