He singlehandedly did significant harm to her campaign on what should have been a positive night for her. Any conservative would have a tough fight to win in liberal Delaware, and backstabbing from a prominent member of a candidate's own party makes things even tougher.
Rove is a jerk mostly out for himself, and not a team player as he demonstrates with his periodic trashing of Republicans who are not among his favored individuals. And he is a political operative who should not be put on Fox as an analyst or commentator. He always has a personal agenda.
I'm surprised so many don't get it.
Rove didn't do that "singlehandedly". He had a lot of help. Another allegedly conservative pundit, Krauthammer, lit off wailing about O'Donnell's choice almost immediately after her primary victory. I leave the room to fetch a beer whenever that loser comes up on Fox News.