Pretty much whoever she picked as a running-mate.
Who would be running now on both sides, and which Republicans would have run in 2012? Immediately take out Paul, Rubio, and Cruz if you ask me. A President Clinton wouldn't build up nearly the amount of tea party steam that propelled those 3 into office.
Why not? The Clinton's are certainly not beloved by the hard right.
Presumably, a Hillary Clinton presidency wouldn't have brought out all the dog-whistle racism that added to the Tea Party. And it's not like the Republicans could get that much more misogynistic.
So which House, Senate and Govs races would the GOP have not won had Hillary been president in 2008 and 2012?
