ABC News’ Rick Klein reports: Rep. Joe Sestak, D-Pa., today formally announced his candidacy for Senate in Pennsylvania, setting up a primary match-up against veteran Sen. Arlen Specter that will be a political test for the Obama White House. Sestak used his campaign announcement to commit to “change and accountability” — setting up a contrast with Specter, who won his first Senate race as a Republican in 1980. Specter became a Democrat in March to avoid what was likely to be a bruising Republican primary. The announcement by Sestak, a second-term House member from the Philadelphia suburbs, comes despite aggressive efforts by the state and national Democratic establishment to clear the field for Specter. After Specter switched parties, President Obama, Vice President Joe Biden, and Gov. Ed Rendell, D-Pa., all pledged their full support for Specter. Sestak’s candidacy, however, may complicate Specter’s reelection efforts. The loyalties of Obama and other prominent Democrats will be tested, now that a credible Democratic challenger is in place. “It would be disappointing [if] the Washington political establishment of my party — which, and I respect those individuals in it . . . dictated who would be anointed to be the primary candidate,” Sestak said on ABCNews.com’s “Top Line” in June. The winner of the Democratic primary is likely to face former Rep. Pat Toomey, R-Pa., who narrowly lost a primary challenge to Specter in 2004.