The difference between the almost right word & the right word is really a large matter--it's the difference between the lightning bug and the lightning. ~ Mark TwainJohn McCain has taken to calling the Republican crusade against Islam a "transcendental challenge." Transcendental describes something that is extravagant, often in an abstract or supernatural way. Baby Boomers will remember the Transcendental Meditation that was all the rage on college campuses in the 1970's. A transcendental challenge is using the force to levitate your X-Wing fighter.
I suspect McCain means to use the word transcendent, meaning exceeding normality. Using the wrong word like this is a common error of a lazy speaker, someone who chooses big words he doesn't understand because he thinks it will make him sound intelligent.
See also Stephen Colbert.