Sestak is fond of what he calls “metrics.” His campaign measures everything, even the number of brochures its volunteers distribute. The long hours his district office is open produce a different set of metrics. “I’ve got more than 1,000 constituents who are losing, or who are in danger of losing, their homes who have walked into that office over the last four years,” he said. “But the first year, there were only 49. You have to think about the people behind those numbers. My party just didn’t get it. The leadership didn’t get it. These people out there were being slammed, and we were doing things to help them, but the people didn’t feel it. I understand the art of the deal, I really do. But we lost people because it looked to them like the whole point of it all was the deal itself.”

The House recently passed legislation that would prevent special-interest groups and corporations from anonymously sponsoring political advertising, intended as a corrective to a Supreme Court ruling that loosened the rules of campaign giving. But Democrats in the House fashioned an exception for the National Rifle Association and a handful of other groups.

Sestak volunteered this episode as an example of what he detests in Washington, although he did ultimately vote for the bill. (His anger, it should be made clear, was not directed at the N.R.A. but at his own party leadership.) “That deal making for the N.R.A., and the carving out of that, was the worst of sausage making,” he said. “Oh, my gosh, in the end you’re forced to vote for something so bad, I told them I wouldn’t vote for it. And they went back and made it a little more amenable, but it was outrageous what they did.”

SESTAK IS FAR from a natural orator. When emphasizing a point, he has a habit of elongating syllables, words and whole sentences, which can make him sound like an old vinyl record running too slow on the turntable. He sprinkles his remarks with reams of statistics. Some people assume he’s humorless, but I did not find that to be the case. As we were sitting in an outdoor arena watching the truck pulls at the county fair, with gears grinding and engines roaring, he leaned over to me and said, “I guess this isn’t where I should tell people about the hybrid I drive at home.”

Several times, Sestak mentioned to me the average age of the 5,000 or so sailors on the aircraft carrier he commanded: 19½. He felt responsible for their security and development. I got the sense that politics serves a need of his to feel that he has an impact on the well-being of large groups of people. Perhaps because of his military background, the way he connects to voters is partly through his physicality — his running of the parades, the grueling hours and self-induced deprivation of campaigning.

“You remember that trip we took?” he said to an aide, Chip Ridewood, in early July. He was harking back to the voyage he undertook to decide whether to challenge Specter. Ridewood sort of winced, indicating his memories might not be quite as pleasant. “It was great, a great tour,” Sestak said. “Sixty-seven counties, three weeks. We just about lived in that car, didn’t we, Chip?”

Over the next two and a half months, Sestak may have to sometimes fly around the state, rather than driving, as he does now, sometimes through the night — though his campaign says he has no plans to change his mode of travel. Tens of millions of dollars will be spent on advertising for the Senate contest in Pennsylvania. Sestak won’t be able to will himself to victory through sweat and effort, but he seems to see value in demonstrating that if he could, he would. At the Canonsburg parade, as Sestak was running uphill, a man on the side of the road shouted: “Slow down, Joe! You’re not even halfway there!” Sestak turned in his direction and made eye contact, seemed to slow for a moment and then took off at a faster pace.