“We’ll do plenty of stories,” Mr. Trump promised enigmatically. “O.K.?”  [NYT, 6/7/16]

With all due respect to reporters Jason Horowitz, Alexander Burns, and Maggie Haberman, enigmatically is not the word you’re looking for.  Enigmatically implies there is a secret reality that is being concealed.

There is no secret reality.  Trump has nothing in his head but the words that come out of his mouth. The word you’re looking for to describe Donald J. Trump’s response is cluelessly.