See "prohibition."
Some years later, no amendment needed to prohibit a recreational drug.
Feds credibility on this issue is below zero.
When you stand trial and a jury of your peers finds you guilty, they will have credibility.
When the government seizes your property and sends you to prison, where you live in a tiny cell with murderers and rapists, they might start to have some credibility.
When your arrest and sentencing is published in the local paper, along with others just like yours, and no one cares...you get the idea.