Well, if you can find something that says a constitutional amendment for Prohibition was required, I'd be very interested in reading it.
"An amendment to the Constitution obviously appealed to temperance reformers more than a federal statute banning liquor. A simple congressional majority could adopt a statute but, with the shift of a relatively few votes, could likewise topple one. Drys feared that an ordinary law would be in constant danger of being overturned owing to pressure from liquor industry interests or the growing population of liquor-using immigrants. A constitutional amendment, on the other hand, though more difficult to achieve, would be impervious to change. Their reform would not only have been adopted, the Anti-Saloon League reasoned, but would be protected from future human weakness and backsliding."
Thomas Jefferson prohibited liquor sales to the Indian tribes in 1802 without an amendment. His Secretary of State at the time was James Madison -- the man who wrote the U.S. Constitution. I think Madison would have informed Jefferson if he was acting unconstitutionally.
"Massachusetts colonial laws (1660 to 1672) restricted the sale of liquor to Indians. Pennsylvania and New Jersey passed similar laws. On January 28, 1802, president Thomas Jefferson asked the United States Congress for a prohibition of “ardent spirits” among Indians for the “benefit of Indians” and “to keep peace.” The Act of March 30, 1802 (Sec. 21, 2 Stat. 139, 146), gave authority to the president to “prevent or restrain the distributing of spirituous liquors among all or any of the said Indian tribes.”
Me too.