If the numbers drop too low, the legitimacy of the system is at risk. Consider midterm congressional elections, when turnout runs only about 40 percent, or local elections that sometimes dip shockingly low.
How seriously Americans take their presidential votes was illustrated this year by the effort and time that many devoted to obtaining the photo identification required under new laws in some states.
"Every four years we are divided, Republicans and Democrats, by real differences -- in what we feel government should be doing and so forth -- but we are united in this responsibility to keep America going and the privilege to participate in it,'' said Lanning, the psychology professor.
For many, it's a family tradition.
Kelvin Lovely's grandmother always encouraged him to vote, and he took it to heart. The 42-year-old Pensacola, Fla., resident cast his first ballot at 18 and became a regular. "I always want to vote, and I think my vote will have an impact,'' Lovely said.
Veronica Padilla of Las Vegas is already stressing the importance to her 13-year-old son, five years before he can vote.
"I tell him not to just vote for the most popular,'' she said. "You have to stand for what you believe.''
Tim Farmer, a University of Denver law student, attended a Romney rally one day and an Obama event the next because he feels a responsibility to make the right choice.
"Enough wrong votes,'' Farmer said, "and you get the wrong guy elected.''
Adam Brandstetter knows he won't affect the election's outcome. His vote is going to long-shot Libertarian candidate Gary Johnson. "It won't ever matter,'' said Brandstetter.
But he enjoys the sense of community on voting days in Crystal Lake, Ill., a far suburb of Chicago. Brandstetter will leave the home office where he works as an investment manager and head for the polling place at the Lutheran church, staffed by some of his older neighbors.
"I'll take a walk over,'' he said, "have lunch, see all my senior friends: `Haven't seen you in a while. What have you been up to?'''
It feels good to vote, Brandstetter said, and to make time to appreciate that "we're in America. We have the freedom to express our views.''