McCain supporters fueled Hillary's Indiana win
The exit polls show that Hillary Clinton only won Indiana because of pro-McCain voters. In other words, she probably owes her victory to Rush Limbaugh and his army of chaos-loving Dittoheads.
P.S. In fairness, Ben Smith points out that "presumably many of these were voters sincerely picking a second choice." That's true, and it's a good point. It's impossible to know, of course, what percentage were doing that, and what percentage were "playing tactical games," a la Limbaugh. Nevertheless, whatever their motivations, it seems (if we believe the exit polls) that Hillary owes her margin of victory in Indiana to the support of people who have no intention of voting for her in November. Given the Clinton camp's penchant for using primary results to draw conclusions about electability, this seems a fair and pertinent point.