I would say the who the Senate nominees are matters more.
In competitive Senate races Romney ran ahead of
Jeff Flake AZ (Only Winner on this list)
Josh Mandel OH
Connie Mack IV FL (Semi competitive)
George Allen VA
Tom Smith PA
Rick Berg ND
Denny Reberg MT
Pete Hoekstra MI (Semi competitive, God how GOP Senate in Michigan have blown it the last 2 times, damn)
Dick Mourdock IN
Todd Akin MO
Tommy Thompson in WI had a slightly lower % of the vote but lost by a couple points less.
The only Republican to win in a State Romney lost was Heller in Nevada, who got about the same vote % as Romney.
In Texas Romney and Cruz won by a nearly identical margins.
The only candidates to run ahead of Romney in competitive races
Wilson NM
Brown MA (Probably would have won in a midterm)
McMahon CT (Semi competitive, if she had faced Murphy in 2010 instead of Blumenthal she may have won)
Lingle HI (theoretically semi competitive but wasn’t really)
Scott Brown.
if he ran in 2013 in the special against Markey, I say he wins. Then he wins in 2014, right? WHo did the DEMS have to run in 2014 vs Brown? Lynch might have gotten the nomination and been elected.
Brown was popular in MA ... so he moves to NH where he is resented.