Bitcoin in the event of a Government crackdown

I was re-reading an old Mish article on Bitcoin, and read this phrase from Mish:

Yet, should that happen or even be suspected, how long will it take before there is a government crackdown on bitcoin? Should such a thing happen, the value of bitcoin can plunge to next to nothing if confidence is lost.

But hasn’t gold been cracked down by many governments in the past, including the US?  What happened to its value on the black market in these cases?  Certainly, over the long term, we can see that it hasn’t had much impact on the price of gold, other than maybe in the upwards direction.