With this logic, they could say,
The prohibition of murder in the commonwealth and in our country has failed,
The prohibition of assault in the commonwealth and in our country has failed,
The prohibition of rape in the commonwealth and in our country has failed,
The prohibition of theft in the commonwealth and in our country has failed,
The prohibition of driving drunk in the commonwealth and in our country has failed,
The prohibition of hit and runs in the commonwealth and in our country has failed,
No they couldn't; 2 in 3 murders get solved, whereas the fraction of drug "crimes" that even come to the attention of the authorities is doubtless several orders of magnitude samller.