I posted a review of Killing Lincoln today, and thought this idiom was an appropriate selection because of J. Wilkes Booth’s escape from Washington after assassinating President Lincoln. The Phrase Finder describes the meaning as narrowly or barely, and it is usually “…used in regard to a narrow escape from a disaster.” “The phrase first appears in English in the Geneva Bible, 1560, in Job 19:20…’I haue escaped with the skinne of my tethe’.” Escaping by the skin of your teeth means there is no margin for error.