- Replacement of the U.S. Constitution, or any amendment thereto that reduces the rights enumerated in the first ten amendments (Bill of Rights).
- Establishing martial law or a state of emergency within any state without the consent of the legislature of that state;
- Requiring involuntary servitude, or governmental service other than a military draft, for anyone of any age, except in punishment of crime (13th Amendment).
- Surrendering any power delegated or not delegated to a corporation or a foreign government.
- Federal Reserve Bank policy that induces a hyperinflation (a depreciation of the U.S. dollar at an annual rate of 20% or more).
Update Sept. 24: Russell Longcore at DumpDC offers a concurring opinion. He believes that it will take a trigger like the ones listed above to enable a state to secede successfully. The one he considers most likely is #5.