yes, but anyone who went to war with the US and had them would use them. I don't think anyone has any illusions that a nuclear state would sit on their biggest offensive and defensive assets and let the enemy overrun them and topple their gov't. Thats not a truly rational assumption. Indeed, its optimistic, and we can hope nobody would use them. But I'm quite sure if all the US forces were gathering along the Russian border for a similar invasion, one, the troops would be hit with tactical nukes preventing the invasion, then secondly it would escalate with a full nuclear exchange. I don't think we want to even think about what it means for a world power to go to war with another world power in the modern era. Its unthinkable, and only leads to one devistating conclusion. A conventional war between two such powers doesn't seem very likely. If anything, the fact that any strike would lead inevitably to a nuclear retaliation is the reason such a strike won't happen (at least under normal conditions).
MAD was very successful at preserving relative peace. Lets hope it continues to keep powerful nations in line.