James Madison on those who never let a crisis go to waste:

“[Y]ou will understand the game behind the curtain too well not to perceive the old trick of turning every contingency into a resource for accumulating force in the government.”

It’s also in this book here: http://books.google.hn/books?id=w9l2AAAAMAAJ&pg=PA7#v=onepage&q&f=false

As for “never let,” go here: http://www.brainyquote.com/quotes/quotes/r/rahmemanue409199.html