>>“A president must serve only the common cause of the people of the United States.”<<
A believer serves God first - 1 Cor 10:31 - “So, whether you eat or drink, or whatever you do, do all to the glory of God.”
**Disclaimer - I do not equate Mormonism with Christianity, I am speaking in general terms regarding any public official who professes belief**
A president is employed by the people of the country, in the same way that you are employed by your employer. You and I both have a duty to our employer, but I as a believer my chief duty is to God. If my employer asks me to do something that is contrary to my belief, I refuse to do so.
One who has firm beliefs does not put them on a shelf when he punches in. Joseph, Daniel, Esther were all believers in positions of authority in pagan lands. They did not compromise their beliefs in order to serve “the common cause of the nation”, nor should anyone else.