it is fun to listen to everyone bicker about whether he was more Rep or Dem...and he's switching to better match his "liberal" voting record et al. Since elected, up until this last term, he had no competition in primaries. Last go round he barely survived. The Dems long ago gave away winning that seat...so there are no real candidates in that party to compete.
Has nothing to do with the state switching..its all about him staying in by minimizing the competition. It may very well backfire, should Philly turnout for the off-term election not run at 85-95+%..which is what is needed for a D to win.