Rep. Parker Griffith (D-AL-5) is expected to announce today that he is switching from Democrat to Republican:

According to a senior GOP aide familiar with the decision, the announcement will take place in this afternoon in his home district in northern Alabama.

Griffith’s party switch comes on the eve of a pivotal congressional health care vote and will send a jolt through a Democratic House Caucus that has already been unnerved by the recent retirements of a handful of members who, like Griffith, hail from districts that offer prime pickup opportunities for the GOP in 2010.

The switch represents a coup for House Republican leadership, which had been courting Griffith since he publicly criticized Democratic leadership in the wake of raucous town halls over the summer.

Griffith did vote no on the original House health care bill, so this decision won’t really have any affect on that.