Melania Trump - until now only a minor presence on the campaign trail - found herself caught in an embarrassing plagiarism controversy on Tuesday after a prime-time defense of her husband that appeared to be lifted in part from a speech given by first lady Michelle Obama.

No sooner had the poised 46-year-old former model delivered her keynote address to cheering delegates at the Republican National Convention than the unmistakable similarities to a passage from Obama's speech to the 2008 Democratic convention came to light.

In both passages, the women are introducing themselves to the US public by speaking of the values that have shaped their lives.