Why is Congress so polarized, so gridlocked today? In part, it is because incumbents so rarely have to answer to the American voter.

In the past decade, 78% of the seats in the U.S. House of Representatives did not change party hands, even once. One expert says as few as 20 races can be considered toss-ups next year, out of a total of 435 seats in the House.

CNN's Drew Griffin investigates how “gerrymandering” locks in super-safe seats for many congressmen. This 200-year-old term is the name applied to drawing weird district designs so politicians can pick the voters they want, not what you may want.

CNN’s one-hour documentary “Gerry-Rigged: Why Your Vote Might Not Matter” airs on CNN Presents this Sunday, November 20th at 8 pm ET, replaying at 11 pm ET and 2 am ET.