Joseph Sestak

FOLSOM — Three years after he knocked off a veteran House incumbent, Democratic Rep. Joe Sestak will seek a bigger prize and challenge Republican-turned-Democrat Arlen Specter for his long-held U.S. Senate seat.

Sestak, a former Navy vice admiral, announced his Senate candidacy Tuesday at a crowded VFW hall in his suburban Philadelphia district, near his hometown. He then began a two-day, five-stop swing through the state.

Standing with his wife, Susan, the second-term representative vowed to put "principles over politics."

"We must restore the promise of the American Dream — that our children will have the opportunity, based upon their talents, to do even better than their parents," Sestak said. "Let's again lead this world by example and not intimidation."

In April, the five-term Specter severed his decades-long ties with the Republican Party to become a Democrat. He said, in part, it was to avoid a Republican primary challenge from former Rep. Pat Toomey, who nearly beat him in the 2004 primary.

Sestak, 57, is challenging a White House-backed candidate who has millions more in the bank. But Sestak enters the race with enough money to get off to a competitive start, and he has the potential to give Specter, 79, a serious run.

Much of Sestak's organizational and financial support would likely come from those in the liberal wing of the Democratic Party who have been slow to embrace Specter.

Sestak's announcement had been expected. He has been campaigning and already visited each of the state's 67 counties.

A recent Quinnipiac University poll showed Specter and Toomey in a close race, while Specter had a significant lead over Sestak.

Specter's campaign manager, Christopher Nicholas, on Tuesday denounced Sestak's "taxpayer-financed self-promotion tour around the state" and criticized the congressman for missing 105 House votes this year.

Specter has the advantage of backing from much of the party establishment. President Barack Obama and Gov. Ed Rendell, both Democrats, have pledged support. On Monday, his campaign released the names of more than 100 party leaders who have endorsed him.

Toomey's campaign issued a statement Tuesday welcoming Sestak to the race and calling him "a consistent liberal who really believes in his values," as compared to Specter, "a career political opportunist who believes in nothing but his own re-election."