Definition: "being not quite one of us"

This is an anagram - look for an indicator word that suggests mixing or rearranging letters

'terrible' is the anagram indicator - rearrange the letters of 'OH NO A TRUMP' to form a 10-letter word

Answer: PROTOHUMAN | 'terrible' indicates anagram - rearrange the letters of OH NO A TRUMP to get PROTOHUMAN (being not quite one of us)