The barbs turned personal during Tuesday's primary battle in Indiana. Trump claimed another victory, and Cruz suspended his campaign. What will these results mean for the big picture?
Saturday's Republican primary race in South Carolina gave a big boost to political outsider Donald Trump, and left many Republicans stunned when the establishment candidate, Jeb Bush, dropped out of the race. Geoffrey Cowan's new book traces the history of the presidential primary process from its first days in 1912.