Mencken is a hero for three reasons: his anti-Semitism, his German ancestry, and his founding of a magazine that became (long after he left it) an viruently anti-Semitic and ultimately an avowedly national socialist publication.
Bryan was a species that's all but died out today: A Christian Fundamentalist Leftist. His ideas are vertiable sourcebook on 20th century liberal economic policy.
Unfortunately, today's Fundamentalists allow economic conservatives to determine conservative policy and have come to place free enterprise and small government ahead of genuinely important matters like G-d's Law. Plus the Left has put immorality and freedom from G-d ahead of any economic program.
As to whether Bryan was a Leftist, that is debatable. Was Huey P. Long a Leftist? Was Father Coughlin a Leftist? Was Congressman Louis T. McFadden a Leftist? Was William Lemke a Leftist? Was Charles A. Lindbergh Sr. (of the Minnesota Farmer Labor Party) a Leftist? Was Dr. Francis Townshend a Leftist? Were the Populists of the late nineteenth century Leftists?
The fact is that many "palaeocons" look up to these people as fighters against "Jewish international bankers" or "the Insiders" and they get a pass for their "leftist" economics.