Arlen Specter feared losing a Republican primary to Pat Toomey in 2010. Specter defeated Toomey by just 2% in the GOP primary in 2004, and Republicans in Pennsylvania were not thrilled with Specter voting for the stimulus bill in February (one of only 3 Republican Senators to do so).
Toomey led Specter by a big margin in early polling. So Specter decided to become a Democrat, giving the Democrats their 60th vote and filibuster poof majority in the US Senate. The Obama administration and state Democrats welcomed Specter with open arms. Nonetheless, Democratic Congressman Joe Sestak, first elected in 2006, decided to enter the race to challenge Specter, though the Senator had a big bankroll and support from national and state Democrats.
Now just a few months after his party switch, Pennsylvania voters seem to regard Arlen as Arnold (as in the traitor Benedict Arnold) and the Senator is in danger of a defeat by Pat Toomey in a general election matchup in November 2010. Toomey leads Specter by 48% to 36%, and Specter's once huge lead over Sestak is now down to 13% in the Democratic primary race (47%to 34%). If Sestak, who has raised $ 3 million already, defeats Specter in the primary, and becomes the Democratic nominee, he too trails Toomey at this point by 8% (43% to 35%). Barack Obama carried Pennsylvania by just over 10%, but opposition to Obama's health care reform bill seems to be a key factor in fueling Toomey's early strength in the 2010 race.
Pennsylvania has the second highest percentage of the population over age 65 in the country, and elderly voters around the country perceive they will be the ones who will have to sacrifice to pay for the provision of health insurance to the 46 million not now covered.