Claims are easy, credible evidence not so much.
One of the reports I saw said a "nuclear powered" cruise missile. Pretty much everyone gave up on nuclear powered missiles or aircraft decades ago - granted if you could make one work it would have nearly unlimited range but just to make something workable would be groundbreaking - making it fit on a cruise missile would be earth shaking.
I wonder what part of "MAD" Putin is forgetting? The USA still has a plentiful supply of instant sunshine that could be quickly rained on Russia.