Sherrod Brown lives in a white-ish state but a large portion of his constituents are black and he has to rely on their turnout to win. Maybe black people in Ohio are different than those in the south, but he has the best shot of any northern white dude who might run.
That isn't to say he has it locked up, but he probably could at least keep the margins better than Bernie did if he was against a candidate who was strong there. Depends on how he plays his campaign I guess.
I don't think we need to run a white guy, even though that might help. If Duckworth can win midwesterners like Obama did I think she could be a strong candidate, though I'm unfamiliar with her otherwise so she might be a stinker on the national level. Klobuchar is probably a little too conservative to win the primary but she'd probably be strong in a general election. There's also Harris and CCM both showing interest, of course, which is "bank on AZ/FL/NC" type of run, which I'm skeptical of but that's probably their most electable strategy. Or maybe they'd actually connect really well with voters in Iowa and Minnesota, I don't really know. Where's Aaron to back up how great Brown is.