Is it ever proper to call the President Mr Smith as opposed to President Smith or Mr President?

It is generally considered improper to refer to the President simply as "Mr. Smith," as this can be seen as disrespectful and diminishes the office's dignity. The appropriate titles are "President Smith" or "Mr. President," which acknowledge the individual's position and authority. In informal contexts or private conversations, the use of "Mr. Smith" might be acceptable, but in formal settings, the respectful titles should always be used.