I would suggest rather than quizzing them about policies, ask them more about why they don’t like Trump. This will trigger and reinforce their values - and help them to reject Trump.

Eg: “Well, I don’t like it that he lies.”
-oh, and would you trust someone you knew lied as your spouse, or doctor, or business partner?

Eg: “I don’t like his attitude toward women”.
-oh, what kinds of things have you heard him say that you disapprove of in someone supposed to be a leader and a role model?

These conversations allow them to explore their values more deeply, and maybe come to the conclusion Trump is not someone they could cite for with integrity.