I found the exact words but not where they are from or when. Here is the quote
“It turns out that our founders designed a system that makes it more difficult to bring about change than I would like sometimes.”
http://www.freerepublic.com/focus/f-news/2843848/posts
http://www.wnd.com/2012/02/savage-founders-envisioned-petty-dictator-like-obama/
Obama told NBC’s Matt Lauer Sunday that “people” have been “frustrated” that “I have not been able to force Congress to implement every aspect of what I said in 2008.”
“Well, you know,” the president continued, “it turns out that our Founders designed a system that makes it more difficult to bring about change than I would like sometimes.”