I would go the other way. I would say “This is the last time I will address this issue. It has been asked and I have answered numerous times. I will no longer address this question.”
drop the mic and walk away...
I don’t think that’s Trump’s style. I think he’s at his best when takes an attack and turns on the offense with both barrels. And this one forces the Democrats to try to debunk all Trump’s “lies” about their history. The best they can do is say “We’re not that racist.”