Updated: 1:13 p.m.Sen. Arlen Specter (R-Pa.) announced Tuesday that he is switching parties and will run for re-election as a Democrat in 2010, drastically altering the balance of power in the Senate. “Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right,— Specter said in a statement. “I now find my political philosophy more in line with Democrats than Republicans.—One Democratic source said Senate Democratic leaders have been working Specter for weeks and that they have promised Specter that the Democratic Senatorial Campaign Committee would not run anyone against him in the Democratic primary. A spokesman for the DSCC declined to comment on that matter. Specter has been a Republican for more than 40 years. His switch would make him the Democrats’ 60th vote in the Senate if Democrat Al Franken — in the midst of a legal recount battle in Minnesota — is seated. But, he cautioned in his statement, his change in party affiliation does not mean he will be a “party-line voter— for the Democrats.“Unlike Senator [Jim] Jeffords’ [Vt.] switch which changed party control, I will not be an automatic 60th vote for cloture,— Specter said. “For example, my position on Employees Free Choice (Card Check) will not change.—Specter’s switch comes as he faced an increasingly unfavorable electoral environment in Pennsylvania. The Keystone State Senator faced a competitive primary challenge from former Rep. Pat Toomey (R), who came within 17,000 votes of defeating him in their 2004 matchup. Recent public polls showed Toomey ahead of Specter by double-digit margins. The same public polls, however, showed Specter with high ratings from Democrats — 71 percent compared with 36 percent approval from Republicans, according to a March poll from Quinnipiac University. If he had run for re-election as a Republican, Specter would have had to mount a massive voter registration drive to switch Democrats to Republicans for next year’s closed primaries. In his statement, Specter said he was making the move now because of his upcoming re-election. “I am taking this action now because there are fewer than thirteen months to the 2010 Pennsylvania Primary and there is much to be done in preparation for that election,— Specter said. “Upon request, I will return campaign contributions contributed during this cycle.—Emily Pierce contributed to this report.