Tell him that attacking the source of the information is not a valid argument, and in doing so, he’s showing intellectual laziness.
Appeal to his natural youthful liberal arrogance.
He has to refute the points on their own merits.
you make an excellent point-
tell him to counter your arguments with facts of his own, not simply counter them with “you’re facts are wrong because you got them from poopyheads”
ask him to prove they are wrong on his own
(libtards are not taught how to do that, so you will have to stress that college is supposed to teach you HOW to think, not WHAT to think)