Complex sentence: Brown researched the source of Rogers'ability to be persuasive and authoritative and concluded that it arose from Rogers' ability to embody and reflect characteristics that the U.S. public associated with the American dream.
Split into simpler sentences: Brown researched the source of Rogers'ability to be persuasive and authoritative. He concluded that Rogers' influence and popularity arose from Rogers' ability to embody and reflect characteristics that the U.S. public associated with the American dream.