I found a page to what must be the German analogue of Elmer Gantry on wikipedia today. It’s called “Der Untertan”

Der Untertan is the most famous novel by German author Heinrich Mann. It has been translated into English under the titles “Man of Straw,” “The Patrioteer,” and “The Loyal Subject” (translation by Helmut Peitsch). The title literally means ‘The Subject’, in the sense of an individual subjected to the rule by an elite.

Although the novel was completed in July 1914, shortly before the outbreak of World War I, it was not published until 1918 (by Kurt Wolff Verlag of Leipzig). After the war, the novel enjoyed considerable popularity, given its critiques of the ultra-nationalism of Wilhelmine Germany.
“Der Untertan” portrays the life of Diederich Hessling, a slavish and fanatical admirer of Kaiser Wilhelm II, as an archetype of nationalist Wilhelmine Germany. Hessling is unthinkingly obedient to authority and maintains a rigid dedication to the nationalist goals of the German state.
Throughout the novel, Hessling’s inflexible ideals are often contradicted by his actions: he preaches bravery but is a coward; he is the strongest proponent of the military but seeks to be excused from his obligatory military service; his greatest political opponents are the revolutionary Social Democrats, yet he uses his influence to help send his hometown’s SPD candidate to the Reichstag to defeat his Liberal competitors in business; he starts vicious rumors against the latter and then dissociates himself from them; he preaches and enforces Christian virtues upon others but lies, cheats, and regularly commits infidelity.