POLITICO has learned that Rep. Parker Griffith, a freshman Democrat from Alabama, will announce today that he’s switching parties to become a Republican. According to two senior GOP aides familiar with the decision, the announcement will take place this afternoon in Griffith’s 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.