1. No. There are too many possible ways to avoid or prevent "Launch under attack" (especially with all those holes in SBIRS-HEO system and Biden-in-the-loop vulnerability) . That's why US Government don't rely on it. Read GDP, please.
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One Ohio has twenty Trident-II missiles, few of them with one W76-2 5kt warhead each, and 18 with, say, 3 W76-1 90kt warhead each.
It means 54 90 kt warheads and 2 5 kt ones.
It means, that you can't attack Moscow at all (its ABD can intercept 200 incoming warheads), you can attack few less important and, therefore, lesser defended cities (like Vladivostok or Saratov) with their population partially evacuated and partially sheltered.
And it means, that your relation strike definitely won't "wipe out Russia" and even won't make their "aggression against Ukraine (or against the USA, for that matter) " unprofitable.
Under what circumstances the USA can leave Alaska or Texas? More or less same are circumstances in which Russia can leave Crimea and Novorossia.