Why can't Americans vote online?

(CNN) -- Tuesday is Election Day in the United States, and although the mostly state and local races won't stir the same passions as next year's presidential contest, millions of people will cast ballots.

They'll do it in much the same way that Americans have for centuries: by showing up at a polling place and ticking off boxes for their candidates of choice.

All of which raises the question: In an era when virtually every daily task can be done on the Internet, why can't we vote online, too?   Full Read