Reply #2: You take two leaps of logic with which I don't really agree.

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You imply that they're picking centrists to win these races. I'm not sure that's what's guiding them.

They're pikcing candidates they think can win, regardless of their politics.

Santorum is an incumbent US senator with national aspriartions in a close state. The Democrats picked to beat him a candidate who set a record for votes in a statewide race in Pennsylvania. They are picking someone a lot of Penn'ians like. Trying to increase the margin of victory by picking a popular candidate is a good idea. You might feel like the point is to get rid of progressives. But if there were a progressive whom everyone liked, that progressive would be on the ticket. Furthermore, a LOT of progressive Democrats voted for Casey in his statewide race. He won progressive Philadelphia districts be a margin as big as he won conservative eastern PA districts.

I don't know about the two Congressional represenatives, but I suspect that it's the same story.

And why are the Democrats working so hard? Because the senate is a few seats away from being dominated by the hard right. Any resulting centrism of Democratic strategy is motivated by the desire to avoid being dominated by the hard right. I don't have a problem with that.

Your second leap of logic is that democrats would use the elections to sell centrism. I'm not sure that's the case. The democrats don't want to alienate the progressives in the party, so why would they crow about centrism?