Eye on 2010

Pennsylvania Democrats thrived in the past few election cycles. Barack Obama carried Pennsylvania last year by a comfortable 10 percentage-point margin over Republican John McCain, giving the Democrats their fifth consecutive presidential election win in the state. Term-limited Democrat Edward G. Rendell is rounding out an eight-year tenure as Pennsylvania's governor.

The Democratic Party also controls 12 of 19 U.S. House seats in the state, after a five-seat gain over the past two election cycles -- even though the congressional map was redrawn by Republican legislators prior to the 2002 elections and was contested by Democrats in court as unfair.

"These are dark times for the Republican Party, which has had a rich tradition in Pennsylvania," said Christopher Borick, a political scientist at Muhlenberg College in Allentown. "Every party has ups and downs, but this, to use a market analogy, appears to be a bottom for them."

Specter's switch, whenever it becomes effective, will put Democrats in operative control of 59 seats, compared to 40 for the Republicans -- and one in Minnesota that is still vacant because former Republican incumbent Norm Coleman is staging a long legal challenge to an apparent but razor-thin victory by Democrat Al Franken in last year's election. The Democrats' number includes the Senate's two independents, Vermont's Bernard Sanders and former Democrat Joseph I. Lieberman of Connecticut, both of whom caucus with the Senate majority.

The Democrats held a roughly similar 59-41 edge in the Senate in 1979, one year before Specter was first elected. But just to illustrate how much has changed in Northeastern politics, the Republicans then held both Senate seats in Pennsylvania and one in New York, plus one seat apiece in five of the six New England states. Today, the Republicans control just three Senate seats in those eight states -- two in Maine (held by Olympia J. Snowe and Susan Collins) and one in New Hampshire (held by Judd Gregg, who's not seeking re-election next year).

Specter's announcement of his party switch came just four days after Republican James Tedisco conceded the closely contested March 31 special election in New York's 20th District, a rural and exurban area near Albany that until recently had a long history of voting Republican.

Democratic businessman Scott Murphy won the seat formerly held by Democrat Kirsten Gillibrand, who was appointed in January to fill a Senate vacancy, and his victory put Democrats back in control of 26 of 29 House seats in New York. In the 2008 election, the Democrats also won all 22 House seats in the nearby six-state New England region.