It was big news when our national debt recently passed the $20 trillion mark. What's less understood is exactly why having such a massive debt is a bad thing. The short answer is that too much debt slows economic growth, reducing living standards.

The sheer size of the existing debt is deeply worrying to economists on both the left and the right, who agree that when debt reaches 90 percent of GDP for five years in a row it means painfully slow growth, creating what's called a "debt overhang."

Edited by Mark McDaniel. Written by Nick Gillespie. Graphics by McDaniel and Meredith Bragg. Cameras by Jim Epstein and Alexis Garcia.