HAHAHAHAHAHAHAHAHA
What makes you think they'll need another Constitutional amendment? They haven't needed one for the war on drugs. In what way is alcohol any less dangerous a drug than marijuana?
The only reason we had a Constitutional amendment back in the day is because people of the time were capable of actually reading and understanding the Constitution. After a hundred more years of public education, that particular problem has been eliminated.
And greatly reduced even among FReepers, as witness the loud approval for the War on Non-alcoholic Drugs.