There is a reference in the film to the Wickersham Report and that was the report issued by a Committee convened by President Herbert Hoover on the problems of enforcement of the Volstead Act. That by the way was the standard method by which Hoover addressed problems, he appointed commissions to study it. The Wickersham Committee documented in great detail the onerous and impossible difficulties of enforcing a law the majority didn't want then concluded we have to try harder and Prohibition should be continued.
One result of Prohibition still with us today is the syndication and organization of crime in the USA. Organized crime grew out of the various local criminal elements and the rivalries therein to control the illegal booze traffic. Liquor is legal but criminals to this day find other outlets for their activities. Al Capone in Chicago was the most widely known, but every metropolitan area had their criminal gangs looking to control the illegal traffic.
The Depression may have been the biggest single factor in bringing about the end of Prohibition. Gangsters may be colorful tabloid fodder in good times, in bad times when people are jobless and wondering when the next meal was coming, flaunting wealth was not a good idea. People might not be able to afford much, but a nickel beer was welcome.
Also the fact that illegal liquor was sometimes laced with wood alcohol and other unhealthy substance was a national tragedy. Maybe people couldn't handle their liquor before, but you were not going to go blind, get paralyzed or die with only one drink.
It was a colorful era, but a nightmare as well, foisted upon us by people who always seem to know what's best for the world. In the final chapter Ken Burns documents its welcome end.