ven ak lar. but with martin luther king, he was always respectful. reporter: early in his career he was no civil rights activist. casting votes against the legislation. when he was a senator from texas, he really couldn t follow up that much. otherwise he would have lost his seat. reporter: so what was the driving force behind this momentous moment? many looked to johnson s childhood in texas where he grew up in a fall farmhouse as the eldest of five. he was poor. i think he felt guilty enough and had had enough pain about his own hardship and poverty as a texas schoolteacher. reporter: he was a shrewd dealermaker and politician drawing on his experience in congress. he had lived and breathed and been through a thousand battles