Sen. Arlen Specter of Pennsylvania is switching his party affiliation from Republican to Democrat, said Chris Cillizza in The Washington Post. “Specter's decision would give Democrats a 60-seat, filibuster-proof majority in the Senate assuming Democrat Al Franken is eventually sworn in as the next senator from Minnesota.” It will also improve Specter's own political fortunes.

Don't count on it, said Jim Geraghty in National Review. Republicans already knew Specter wasn't one of their own—former Congressman Pat Toomey would have "beat him like a drum" in the 2010 GOP primary. But Specter still isn't safe—his American Conservative Union rating of 40 makes him too liberal for Republicans, but it also might make him too conservative to suit Democrats.

This still is "probably not a good sign for the future of the Republican Party," said Megan McArdle in The Atlantic. It's not that Arlen Specter was so crucial to the GOP's "ideological or political integrity." But Specter is a "seasoned politician from a swing state." His decision is a sign of which way the wind is blowing.