U.S. Sen. Arlen Specter is a marked moderate. In the Senate, the Philadelphia Republican voted mostly with his party last year, but with the Democrats more than a third of the time. Neither side thinks that’s enough and both want to beat him when he seeks an unprecedented sixth six-year term next year. Conservative Republicans consider him a RINO — a “Republican in name only.” They would like nothing better than if one of their own knocked him off in the Republican primary and took their anti-government, lower-taxes, anti-abortion fight to the Democrats. “I think he’s extremely vulnerable in the...