Growing up in St. Louis in the 1950s and ’60s, Deddrick Battle came to believe that the political process was not for people like him — a struggling black man whose vote, he was convinced, surely would not count for much of anything. The thought became ingrained as an adult, almost like common sense.

But a month ago, at age 55, Mr. Battle registered to vote for the first time.

Senator Barack Obama was the reason.

“This is huge,” Mr. Battle, a janitor, said after his overnight shift cleaning a movie theater. “This is bigger than life itself. When I was coming up, I always thought they put in who they wanted to put in. I didn’t think my vote mattered. But I don’t think that anymore.”

Across the country, black men and women like Mr. Battle who have long been disaffected, apolitical, discouraged or just plain bored with politics say they have snapped to attention this year, according to dozens of interviews conducted in the last several days in six states. They are people like Percy Matthews of the South Side of Chicago, a 25-year-old who did vote once but whose experience was so forgettable that he cannot recall with certainty whom he cast a ballot for or even what year it was. Now an enthusiastic Democrat, he says the old days are gone.