Allow the President to invade a neighboring nation whenever he shall
deem it necessary to repel an invasion and you allow him to do so
whenever he may choose to say he deems it necessary for such purpose,
and you allow him to make war at pleasure....
If today he should choose to say he thinks it necessary to invade
Canada
to prevent the British from invading us, how could you stop him? You
may
say to him, "I see no probability of the British invading us," but he
will say to you, "Be silent; I see it, if you don't."
-- Abraham Lincoln, in an 1848 letter to his law partner, William
Herndon, criticizing Polk's decision to invade Mexico for the purpose
of
preventing future war