This was really the non-race of the year. What happened?
As I say every time Delaware comes up, the DE GOP is one of the most ineffectual state parties in the country. Currently their only statewide elected officeholder (aside from Castle, who already served two terms before Carper and is getting on in years) is the state auditor, who has been in his office for something like 18 years. Their hold on the state house of representatives is looking likely to flip this year. It was looking like Charlie Copeland, their Lt. Governor candidate, was their best hope at salvaging something out of this year, but now it's starting to look like John Brady, who's running for Insurance Commissioner, is their only hope. (Brady, incidentally, is a former Democrat running as a "Progressive Republican".)