Democrat Joe Sestak hopes to get to the U.S. Senate Forrest Gump-style: He's crisscrossing Pennsylvania, walking exactly 422 miles, in his effort to unseat Republican Pat Toomey. His campaign slogan, of course, is "Joe Sestak walks in your shoes."

Sestak, 63, formally announced his bid Wednesday morning in front of Independence Hall and about 75 supporters who braved a sprinkling rain. Dressed in white-and-gray high-top Reeboks, jeans, and a bomber jacket, Sestak said he's running because he's disgusted with Washington politicians.

"The largest deficit is not the debt - it's the trust deficit," said Sestak, a three-star admiral and a former Delaware County congressman. "We just don't trust politicians."

After his announcement, Sestak traded his Reeboks for boots he wore in Afghanistan and began his walk. His first stop: Philadelphia's Vietnam Memorial. His walkabout will take about a month. He'll be updating his website, http://joesestak.com, daily.

This will be Sestak's second run for the Senate, and if he wins the Democratic primary, the second time he will face Toomey.

The 2016 race will have national implications. Democrats see Toomey as one of the three or four most inviting targets in the country as they try to take back the Senate.

At the same time, however, strains between the national party and Sestak exist, and were evident on his first day in the race. Furthermore, some party insiders are already looking for an alternative to Sestak.

Sen. Jon Tester (D., Mont.), chairman of the Democrats' national Senate campaign arm, said he had spoken to "a ton of folks" in Pennsylvania about the race.

Asked whether he hoped other candidates enter the fray, Tester said: "If there's a primary, there's a primary. It's part of the democratic way, right?"

So far, though, Sestak is the only one running.

He told National Journal that he didn't even alert national Democrats to his announcement. He has staffed up with local operatives rather than the national party's hands.

In 2010, Sestak also ran against the wishes of the party establishment, beating Sen. Arlen Specter in the Democratic primary before narrowly losing to Toomey in the general election - a sign, his supporters say, of his toughness and appeal to regular voters, even without backing from insiders.

Sestak ran that year in the face of the GOP's tea party wave, but Democrats expect the playing field to tilt in their favor this time around: Presidential races typically bring out a surge of Democratic voters in Pennsylvania, where Democrats have won the last six.

"Pennsylvania's a very attractive state this cycle," Tester said. "The Democrat has a real chance."

Toomey, however, also figures to be a tougher candidate this time around.

He has had years to build his name, has taken several high-profile steps to soften his image among swing voters - most prominently leading a push for tougher background checks on handgun purchases - and had $5.8 million campaign cash on hand as of his last report.

"I don't pay a whole lot of attention to what Congressman Sestak is doing," Toomey said after a vote Wednesday in Washington. "I'm, as you can see, deeply immersed in my work, which is mostly about economic growth and national security. That's my focus."

Sestak has kept up a relentless schedule since losing in 2010, visiting supporters across the state and building a war chest of $1.6 million, giving him a head start on any potential primary opponents.

Some Democrats, though, chafe at his rough edges and independent streak.

Among them is T.J. Rooney, a former Pennsylvania Democratic chairman and Specter supporter. In an interview last month, Rooney recalled how Sestak railed against the "establishment" in 2010.

"Buck the establishment? Guess what, buddy, a lot of the establishment wants to buck you back," Rooney said.

Tellingly, no Democratic officials came to Sestak's announcement Wednesday. Sestak shrugged it off.

"It's not about the party, it's about people," he said.

Among other Democrats who have considered a run are Montgomery County Commissioner Josh Shapiro, Philadelphia District Attorney Seth Williams, State Sen. Vincent Hughes of Philadelphia, and former Rep. Chris Carney. None has moved to enter the race.

ssmith@phillynews.com 215-854-2611 @sarahesmith23

Inquirer staff writer Tom Fitzgerald contributed to this article.