I expect this will be almost as effective as the banning of narcotics, pirated media, alcohol during prohibition, etc. It's far, far too late for this to have a lasting effect (though certainly a short term reduction is price is likely)
In the big picture, a tension between mathematics and the law has always been near the heart of the history of cryptanarchy and cryptocurrencies. Sometimes-Satoshi-candidate Nick Szabo has written extensively on this for ages [0]. I'd summarize it like this: 1) The Constitution cannot ultimately protect the legality of any crypto-related activity against a motivated governement. 2) The government cannot ultimately stop P2P crypto-architectures from functioning, although illegally, short of shutting down the Internet.