Of course, neither of those two had the advantage of running as an incumbent...
This is true.
The last few 'Rats who managed to actually become incumbents all pretended to be much more centrist than they actually were (Obama, Clinton, Carter).
Of the three, Obama is the one who has really let the mask slip as he heads into his re-election campaign.
My point is that self-acknowledged leftism has been abandoned by the 'Rats as an electoral strategy for decades, and for good reason.