As with anything involving Pennsylvania politics, it’s complicated.

Much of Pennsylvania’s 2010 U.S. Senate race will depend on turnout in the primary and general elections.

Sounds obvious, right? Yet in an odd turn of political and geographical shifts, the Senate candidates will have little control over the outcome.

That is largely because of fiercely competitive primary races on both sides – for Republicans, incumbent Arlen Specter versus former U.S. Rep. Pat Toomey; for Democrats, state Rep. Josh Shapiro versus former Philadelphia deputy mayor Joe Torsella.

In the middle, all of the traditional party organizations will concentrate more of their money and most of their bodies on the governor’s race.

An increased turnout will help Specter in the primary. Yet his voters need one really important thing: motivation to show up at the polls. The governor’s race just might be that motivation.

Toomey’s voters will come out, no matter what. Yet to win, Toomey needs to run a solid campaign with an adult at the helm dictating strategy, not ideology.

Governor's races are defined by the personality of the candidates; voters want to like, know and trust the person who is their governor.

Issues, however, drive federal legislative races.

That helps Specter in a general election but hurts him big-time in the primary. He is seen by the general electorate as a moderate who is not driven by ideology, which is why he was comfortable flip-flopping on the union card-check issue for the short term.

The four clear, credible candidates for the U.S. Senate, in a nutshell: Continued...