Michelle Obama --  August, 2008:
"Barack and I set out to build lives guided by these values and to pass them onto the next generation, because we want our children — and all children in this nation — to know that the only limit to the height of your achievements is the reach of your dreams and your willingness to work hard for them."

The phrasing is very similar, and that is an unfortunate mistake made by Trump campaign speech writers -- because the truth is, Michelle Obama's 2008 remarks were hardly revelatory. 

In performing a bit of research, I uncovered a quote from Will Steger's 1989 book, Crossing Antarctica, which reads strikingly similar to Michelle Obama's:

"As I learned anew in crossing Antarctica, the only limit to achievement is the limit you place on your own dreams.I