From his statement:
…Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right. Last year, more than 200,000 Republicans in Pennsylvania changed their registration to become Democrats. I now find my political philosophy more in line with Democrats than Republicans.
When I supported the stimulus package, I knew that it would not be popular with the Republican Party. But, I saw the stimulus as necessary to lessen the risk of a far more serious recession than we are now experiencing.
Since then, I have traveled the State, talked to Republican leaders and office-holders and my supporters and I have carefully examined public opinion. It has become clear to me that the stimulus vote caused a schism which makes our differences irreconcilable. On this state of the record, I am unwilling to have my twenty-nine year Senate record judged by the Pennsylvania Republican primary electorate. I have not represented the Republican Party. I have represented the people of Pennsylvania.
I have decided to run for re-election in 2010 in the Democratic primary.
I am ready, willing and anxious to take on all comers and have my candidacy for re-election determined in a general election…
He says he won’t be a rubber stamp for the Democrats, and I believe him. He has been willing to stand up to the Republicans in the past. I’m sure he would have been challenged from the right in the 2010 Republican primary; now we’ll have to wait and see if Democratic primary voters will accept his switch. If they believe he has “represented the people of Pennsylvania” rather than the Republican party, he has a shot at re-election.