In a smart review of Geoffrey Kabaservice's splendid, Rule and Ruin, Mark Schmitt discerns a lesson for those who'd like to push the GOP back toward the center:

Ultimately, the moderate Republicans [of the 1960s and 1970s] were losers not because they were moderates, but because they were the truest partisans in recent American politics. They were not ideologues, but the opposite. They put loyalty to party, right or wrong, over their other commitments. Even though many of them eventually switched parties, they almost never leveraged the threat of exit from the party to get their way, whereas conservative Democrats, then and now, always seem to have one foot out the door. Republicans like Specter switched parties only when they realized they had no chance of beating a primary challenge.