Well, I think the theory is that the US defense systems weaken Russian deterrence because many land based ICBMs are vulnerable and would be destroyed in a US first strike. Those remaining could be intercepted to some degree by the US defense system on Russia’s border.
MAD is what sustained Russia in the ‘90s; Paranoia has long been the largest city in Russia.
But, I don’t like Russian Bears in the US underbelly much. I guess their subs are all over the place, though.
Paranoia wasn’t a one way street either.