He realized Edward G. Robinson and Loretta Young could steal films from others easy so he had to make sure his character (who isn't in every scene) counted for a lot. Besides he maintains quite a stiffness through several scenes to make sure his Rankin-Nazi character never becomes too likable (unlike Charlie Kane in Citizen Kane). As for the plausability of the plot. It may interest everyone to know gangster Al Capone's own brother, Richard Hart, was bodyguard to President Calvin Coolidge in real life. Excellent film with (then) state-of-the-art camera angles.