I’ve learned from Wikipedia that from 1919 onwards German soldiers swore the army’s standard oath of loyalty to the German state (Reichswehreid):  

I swear loyalty to the Reich’s constitution and pledge, that I as a courageous soldier always want to protect the German Reich and its legal institutions, (and) be obedient to the Reich President and to my superiors.

Then, in 1933, when Hitler was appointed Reichskanzler, the soldier’s oath was revised to get rid of the “constitution” and “the German Reich and its legal institutions.”

I swear by God this holy oath, that I want to ever loyally and sincerely serve my people and fatherland, and be prepared as a brave and obedient soldier to risk my life for this oath at any time.

Next, in 1935, when Hitler and his Nazis had gained absolute power, the preceding rather vague oath was replaced by one that was narrowly specific, an oath that, for obvious reasons, came to be known as the “Führer oath”: 

I swear by God this holy oath that I shall render unconditional obedience to the Leader of the German Reich and people, Adolf Hitler, supreme commander of the armed forces, and that as a brave soldier I shall at all times be prepared to give my life for this oath.

This Führer oath was used by very many who had sworn it as pretext and camouflage for limitless criminal and savage behavior in the war to come.

These oaths changed from demanding loyalty to country and its institutions, to loyalty to the purposely vague “people” and “fatherland,” to absolute subservience to a dictator. The behavior of Donald Trump’s cultists and of most of the Republican Party seems virtually the same as if they have sworn a Führer oath to Donald Trump. And we have to ask: Can these people truthfully swear to protect and defend the Constitution, when their loyalty to Trump seems to outweigh the demands of truth and morality and true patriotism?