"If we're able to stop Obama on [healthcare], it will be his Waterloo. It will break him." (Senator Jim DeMint, quoted on Politico.com, July 23, 2009)
This brings us to the original Battle of Waterloo where the French Army suffered a major defeat to a coalition of European forces, in 1815, in present-day Belgium.
The French commander, of course, was Emperor Napoleon Bonaparte. Within a month he was exiled to the island of St. Helena, and died there six years later.
Waterloo now means "a decisive or final defeat or setback." Napoleon's loss, it turns out, was our lexicon's gain.