From TPM Reader TB:

I think you may have touched on this before, but I'd like to reiterate the single biggest mental block that currently makes me think I will not cast my vote for Clinton. It makes my stomach hurt to think that in twenty or thirty years I could look back at a list of presidents that includes "Bush, Clinton, Bush, Clinton." This country is far too great to have to rely on two families for so much presidential leadership. Think about it: a two-term Hillary would be TWENTY-EIGHT years of Bush and Clinton. It's petty, but like I said it's a mental block, and I'm just not sure how I can get over it.

I wouldn't call it a petty concern.