They never fully lost it so they didn’t have to regain it. There was certainly some question as to how many of their missiles and nukes would actually work, if push came to shove, but no one ever doubted that SOME of them would work if the Russians ever got pissed enough to light them off.
No risk at all? I’d say '45-'49 was the window that the US could have used nukes on Russia without any fear of nuclear retaliation. Of course, the Russians could have retaliated by invading Western Europe with their massive army, but we didn’t need to fear nukes during that time. After that, there was at least some chance that the Soviets COULD get nukes in from though the 50’s, and it rose from there. At no other time did the US have the ability to strike at Russia with nukes and have confidence that there would be no retaliation though.