[Jim Noble]

What I want to know is this: In 1917, when Congress wanted to restrict consumption of alcohol, they recognized that they had no such power, and the Constitution was accordingly amended to add an enumerated power to Article I.

If Federal alcohol laws required an amendment (since repealed), what gives Congress the power to legislate about weed?

[Mojave]

Congress wanted to restrict consumption of alcohol

Wrong.

Congress wanted to preserve its liquor tax revenues and only yielded to Temperance forces when incumbents started losing their seats.

they recognized that they had no such power

Wrong.

"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." -- Repealing National Prohibition, David Kyvig, University of Chicago (1979)