Laura Bush said in her 2004 RNC speech:

“If you’re determined and you want to work hard, you can do anything you want to. That’s the beautiful thing about America.”

Hillary Clinton spoke similarly in 2014 at the New American Foundation:

“My mother and father gave us a middle-class life with opportunities she never could have imagined for herself but which she always believed could be possible for her children. And that was a great gift that I will be forever grateful for, and then Bill and I of course worked hard to pass on those values to our daughter.”

Ann Romney’s speech was similar in 2012:

“Mitt will be the first to tell you that he is the most fortunate man in the world. He had two loving parents who gave him strong values and taught him the value of work.”

So, I guess if Melania stole someone else's work, others have also.

As for Obama, he clearly plagiarized George W. Bush’s speech in 2014 almost word for word. Yet, the same people attacking Melania Trump didn’t seem to care that he did it. Bush speechwriter: Obama plagiarized Bush - POLITICO