MAD prevented WW3. What do you think happens if the US thinks it can cause significantly more harm to China and Russia through first strikes?
There's no evidence for the existence of such a plan.
And (prior to the invasion) there wasn't even an active plan to bring Ukraine into NATO. It was taken firmly off the table in 2008.
It's just a dictator lying to you, and his own people. It's what they do for breakfast.
This really shouldn't come as any kind of a surprise.
So what your are saying is a falsehood based on the current realities on the ground.
Which, specifically?
I suppose any of the thousands of regular aircraft that Ukraine has "could" deliver a nuclear payload. But that would be a pretty stupid way to launch a first strike, and doesn't change the MAD equation in any way.