I think there are at least two issues being discussed here.
1. He caused O'Donnell to lose. Probably not, AFAIC.
2. Rather than suck it up and take a loss stoically he decided to diss the candidate, IOW, doing the democrat's work for them. He did do that AFAIC.
Because of #2, I wouldn't consider him a person I'd want on my side. Knowledge is good, but wisdom, i.e. knowing when to STFU, is a prerequisite for using the knowledge effectively.
See #136.
Rove helped keep Al Gore and John Kerry out of the WH, while adding House and Senate seats in 2000, 2002, and 2004.
I’m glad he’s on our side.