He also garnered the enduring displeasure of many Democrats after he revealed that the Obama administration had dangled a job to get him out of the race. Rahm Emanuel had asked Sestak's former boss Bill Clinton to extend an appointment to the Intelligence Advisory Board, an unpaid but influential position.
Sestak's campaign remained in perpetual motion, managed by his brother Rich and staffed by some of his six sisters. His offices ran more like hospitals, open seven days a week. A fusillade of press releases was issued at an almost comic pace.
Sestak drove, he talked, he ate little and slept less.
"He's the hardest-working person I've ever worked with," says his media adviser, J.J. Balaban, a veteran of almost 100 campaigns.
In the year of the Republicans and backlash against the Obama White House and Democratic-controlled Congress, Sestak lost to Republican Pat Toomey by 2 points, fewer than 63,000 votes of 3.85 million cast.
So how did Sestak, 59, decide to spend his last weeks in elected office? Revisiting every county in the state.
"I'm going back to say thanks," he tells me. "If the Lord Almighty came down and said, 'Joe, you want to do the last year and half over again, particularly running against the establishment?' I would do it in a heartbeat."
By Thursday, he had toured 40 counties. By Christmas, he hopes to have visited 10 more. On Monday, he's scheduled five stops in Philadelphia.
In 31/2 hours.
In two weeks, Sestak will be out of a job.
He hasn't a clue what he will do. He's had no firm offers.
Sestak hasn't had a job in the private sector since he delivered the Bulletin in junior high.
He can talk. He talks at an astonishing speed and veers off course easily. Kennedy quotes pile up. He still talks as though he were campaigning at some insane pace.
Talking to Sestak, you get the sense that he's walking on one of those airport motorized walkways ramped to some inhuman speed, and that he would be wobbly and disoriented, if not prone to falling over, the moment he had to stop and get off.
He says he can slow down. He looks forward to playing with his 9-year-old daughter, Alexandra, and reading history.
"I'm reading a biography of Andrew Jackson. Here's a fellow running against the establishment, and he was a country bumpkin like me," Sestak says.
"Believe me, I know how to relax, to do nothing," he tells me.
I don't believe him.
Sestak is a better campaigner than a politician. He spent most of his second House term running for the Senate.
The moment he knew he had to stay in the race was "when I met a farmer up there in Potter County. They have a huge billboard that says 'God's Country.' I ask this farmer how he's doing in the recession, and he says, 'Not too bad. I was hurting already so much.' That said it all."
Though Sestak has a Harvard doctorate in political economy and government, "I never used it in the Navy. I was a registered independent my entire career." After 31 years in the military, he defeated 10-term congressman Curt Weldon on his first run for office.
True to the nature of a retired admiral, he accepts responsibility for losing the Senate race. "No one is to blame but me." He's leaving politics having courted many voters but few politicians. He remains an outsider.
"The Democratic Party is the least democratic place," he says. "What will I miss about being in Congress? It's so undemocratic. I watched my party think they were given a mandate two years ago. They stayed down here in an echo chamber and forgot how to communicate. Is it frustrating? Yeah. I think my role was to be a representative first, and a congressman second."
Having been enticed by the U.S. Senate, he's not sure he would run for his House seat in two years, the one that will be occupied soon by Republican Pat Meehan.
"At my age, I'm not the type to go into academia or a think tank," he says. "It proscribes me from speaking my own mind on the issues. I'd still like to make a contribution."
So why the farewell tour? "Because I came so close, I feel it's even more of an obligation," Sestak says. "I'm indebted to you, to the people of Pennsylvania. I was going to do this, win or lose. That's what you do in the military. The battle is over, but you go and thank the troops."
Contact columnist Karen Heller at 215-854-2586 or email@example.com.