By that logic, wouldn't he have also lost in '06? ... '00, '94, '88 ........
A lot of events came together to allow us to beat Lugar. A lot of conservatives in Indiana had been irritated with Lugar for a long time, but there was no real alternative, and that was principally because there was no money.
The Tea Party helped galvanize conservative support around one candidate.
Citizens United allowed Super PACs to fund Mourdock's campaign--without that war chest, it's very unlikely he could have won.
With a credible candidate that had some money, people starting looking more closely at Lugar, something no one had ever done before. No one knew that he didn't have a home in Indiana until this year. Think about that: the guy had been living in DC for 36 years, and no one knew that he didn't have a house in Indiana. Remarkable.
The Citizens United decision was a BFD. Incumbents always had a huge money and name recognition advantage. Super PACs level the playing field. It will be much more difficult for incumbents to win in the future.