Nestled back away from Market Street on an unusually serene plot of Old City, The National Constitution Center’s modern facade projects a scholarly, calm, almost-sterile atmosphere.

But inside, it’s dedicated to a document at the center of some of the country’s most fiercely debated issues. And, as their latest exhibit — The International Spy Museum’s “Spies, Traitors and Saboteurs: Fear and Freedom in America” — proves, a document that has always been and will always be in the spotlight.

“It’s always been an interesting aspect of the Constitution: How do you both protect individuals from harm and protect individuals’ constitutional rights?” says NCC president and CEO David Eisner. “But it’s never been more important than now.”

Starting with the Revolution in 1776, “Spies, Traitors and Saboteurs” looks at how the government and public have responded to domestic threats. While a replica of a globe bomb used during the Chicago Haymarket Riot in 1886 may not spark an immediate connection, other artifacts — such as Ku Klux Klan “business cards” and fragments of the planes that hit the World Trade Center on Sept. 11, 2001 — are very much alive and unwell.