Look, it's not the biggest thing in the world--and I'm not saying it is, it's just kind of annoying. Like if you told me you were the biggest Beatles fan in the world and then you fucked up the lyrics to Let It Be. Just makes him look really stupid.
Because the point isn't that he forgot who said what--it's that that quote sounds NOTHING like Jefferson in terms of language. Like, anyone who's actually read any Jefferson would immediately recognize the anachronism/change in voice. So, yeah, not a reason not to vote for the dude if you like his policies, just a reason to suspect that he's probably not the Constitutionalist he says he is, you know? Wouldn't be a big deal if he was just some regular candidate...