WASHINGTON (AP) — Veteran Republican Arlen Specter of Pennsylvania switched parties Tuesday with a suddenness that seemed to stun the Senate, a moderate’s defection that pushed Democrats to within a vote of the 60 needed to overcome filibusters and enact President Obama’s top legislative priorities. Specter, 79 and seeking a sixth term in 2010, conceded bluntly that his chances of winning a Pennsylvania Republican primary next year were bleak in a party grown increasingly conservative. But he cast his decision as one of principle, rather than one fueled by political ambition as spurned GOP leaders alleged. “I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party,” he said.