Interviewer: don’t you need to uphold the Constitution of the United States as president? Trump: I don’t know

 Presidential Oath of Office:

"I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will to the best of my ability, preserve, protect, and defend the Constitution of the United States."

So Trump is fit to sit in the Oval Office? 

End of story.