The best observation that any politico can offer on the three-way U.S. Senate race in Pennsylvania between Republican Pat Toomey and two Democrats, U.S. Rep. Joe Sestak and incumbent Sen. Arlen Specter, is that it’s complicated.

So many unpredictable dynamics can affect it, including the economy, health care, the war in Afghanistan, and people's perceptions of President Obama, Congress and the two political parties.

Pretend the Pennsylvania electorate is normally distributed in a bell-curve along an ideological spectrum. Now pretend two different scenarios divide the electorate; the candidate with the most people on his side wins, right?

If the candidates are Toomey versus Sestak, the electorate divides more evenly because of where each is positioned relative to the other. When they split the difference between them, they also split the electorate nearly in half.

Villanova professor Lara Brown says that electoral math is why Toomey should prefer Sestak over Specter: “… (If) Specter were his opponent in a general election, Specter might be able to squeak out a win by pulling Democrats who would have no one else to vote for, independents who lean Republican, and liberal Republicans who voted for Specter in the past.”

Toomey should prefer to run against Sestak, in other words, because those former Specter GOP-aligned voters are more likely to side with him.

Sestak is likely to be okay with helping Toomey at this stage because Sestak, first and foremost, wants to be able to have a chance to compete in the general election.

If Sestak does the math, he knows that if he wins the primary, he should be able to win the general election. Even if they split the electorate, the electorate favors Dems at the moment; there are 1.2 million more registered Democrats than Republicans in the state.

Toomey and Sestak also are savvy enough to know the 2010 Senate race will be all about Arlen Specter, not about either of them.

Villanova’s Brown says the centerpiece for either challenger is contrasting his civil campaign with Specter’s crass political maneuvering – first being a Democrat, then running and serving as a Republican, then switching back to Democrat when it appeared he might lose, then being for, against and once more for labor’s Employee Free Choice Act.

“I mean, really,” Brown says. “What is he going to say at the AFL-CIO convention in a couple of weeks?”

Which brings us to Sestak’s huge Obama problem: Next week in Pittsburgh, the president and Specter will address the national AFL-CIO convention; Sestak was excluded. An interesting decision, considering that labor has sent out plenty of mailers to members asking them to elbow Specter on his tepid labor positions. Continued...