The biggest threat to the U.S. lies within, Lieberman writes.
"The attackers on 9/11 never stood a chance against the American people — and outsiders who wish us harm never will," Lieberman wrote for The Hill. "But we have the capacity to destroy our democracy ourselves. Civility is the foundation of a productive democracy."
However, "civility seems to have left our national government," allowing polarization to fester and basic work of the Congress to be stifled, Lieberman writes.
No one will remember where they were when the government shut down, but that was another symptom that doesn't bode well.
"Today, we confront a more tempestuous political environment. The basic rhythms of the national legislative process — the norms that prompted Republicans and Democrats to work together in the service of the greater good — are gone," Lieberman wrote. "Our democracy is proving unable to meet the challenges of the moment. We face real trouble ahead."