John Micek nicely sums up the competing theories:
Rick Santorum’s departure from the presidential race may boost Welch. Many presidential voters excited about Santorum were hoping to buck the establishment and not have a candidate forced on them, Itkowitz writes. Welch, with his support from the state party, is the establishment Mitt Romney character in the Senate contest. But now, those anti-establishment Santorum supporters may sit out the primary. A counter theory is that with Santorum out of the race, the Romney machine won’t be driving a get-out-the-vote effort in key areas, particularly the Philadelphia suburbs, that could have benefited Welch. The winner faces U.S. Sen. Bob Casey, D-Pa., in the fall.
The first scenario seems very unlikely. Primary voters are the most ideological, high-info voters. The people who vote in Republican primaries are more conservative than the Republican general electorate. It seems more likely that Mittheads would stay home now that it looks like he’s locked up the nomination, leaving the rump base to choose the Senate nominee.
My guess is still that Smith and Welch split the southeast vote, leaving Rohrer to consolidate the conservative vote.
What do you guys think?