You’d think that Mr. Sadler would be the kind of citizen-politician who would define the American system, fulfilling its ambition to be a participatory democracy. But it’s only through his own extraordinary efforts to break down the system’s barriers against him that he can even vote, let alone run.

Mr. Sadler grew up near Pittsburgh as a clean-living, law-abiding kid in a family of drug dealers. Shortly after starting college, he was charged with attempting to sell a small amount of crack cocaine to an undercover informant. It was a case of mistaken identity, he said. But he agreed to plead guilty — he was young and afraid, and his court-appointed lawyer told him it was the only sure way to avoid prison.

In 2000, Mr. Sadler moved to Orlando, Fla., with plans to play professional football in the arena league. At the first workout, he ruptured a tendon in his knee. He gave up sports and applied to a master’s program in international business at the University of Central Florida, but his request for financial aid was denied. “And that’s how I found out I was a convicted felon,” Mr. Sadler said. “I had no clue.” The consequences, he quickly learned, were not limited to financial aid. He couldn’t get jobs other than menial labor, and — along with about six million other Americans with a criminal record — he couldn’t vote.

Felon-disenfranchisement laws have had a huge and largely unnoticed impact on American politics, including possibly altering the outcome of the 2000 presidential election. Most were passed in the late 1800s explicitly to keep black people from the ballot box, and today they continue to hurt minorities disproportionately. But lately the tide has been turning, as many states have made it easier for people with criminal records to vote again. In Florida, which disenfranchises more people with criminal records than any other state, voters will decide in November whether to restore voting rights to as many as 1.5 million of their neighbors. And New Jersey lawmakers are considering whether to join Vermont and Maine as the only states to allow people to vote even while in prison.

For Mr. Sadler, the only way to regain the right to vote was a pardon from the governor of Pennsylvania. So he did what anyone with limitless energy and a very good pair of shoes would do: He hand-delivered a clemency petition, walking from Orlando to the governor’s office in Harrisburg. Over 32 days in the dead of summer, he walked 1,178 miles, dawn to dusk daily, sleeping on benches and subsisting on whatever food he could afford along the route. He grew a beard and lost 25 pounds. “That walk was like my pilgrimage to manhood,” Mr. Sadler said. “I looked like Forrest Gump.”