Eternal vigilance is the price of liberty; power is ever stealing from the many to the few. The manna of popular liberty must be gathered each day or it is rotten. The living sap of today outgrows the dead rind of yesterday. The hand entrusted with power becomes, either from human depravity or esprit de corps, the necessary enemy of the people. Only by continued oversight can the democrat in office be prevented from hardening into a despot; only by unintermitted agitation can a people be sufficiently awake to principle not to let liberty be smothered in material prosperity.
January 28, 1852
Speech to the Massachusetts Anti-Slavery Society
[The link about his speech has some interesting history about the frequent misattribution of the “eternal vigilance…” quote.
Also note they had the same problem with democrats then as we do today.—Joe]