> Then the Russians can decide whether they still want to try and the US can decide between being collateral damage or helping Europe. You left out one option

> Then the Russians can decide whether they still want to try and the US can decide between being collateral damage or helping Europe. You left out one option in the the US's decision space: a surprise attack against Europe. I don't think the UK & France combined have enough nuclear warheads to cause an Extinction Level Event without US assistance. But still, if they think the destruction of human civilization is the correct position to take, might be best if we help extirpate them while they aren't sufficiently armed.