Shaheen is no pushover Brown thought she was weak but she is an experienced pol and a far more skilled politician than Brown. I think he severely underestimated her abilities as a candidate he will end up losing badly and embarrassing himself.
I don't think he'll lose by any sort of wide margin, I think it'll end up around Shaheen's 2008 margin (7 points), give or take a point or two.
Brown thought Shaheen would be an easy target because she's from a state that is far more purple than MA and because Shaheen is one of the least bipartisan senators, voting with the majority of democrats about 99% of the time. But apparently her state doesn't care whether she's bipartisan or not, or perhaps they just don't see a former massachusetts senator who lost by 8 despite having a 59% approval rating as being all that better than Shaheen. Republicans should have gone with someone like Judd Gregg or perhaps even Sununu again.... This race hasn't been polled much by reputable companies, and if this is to be another 2010 perhaps Shaheen could go down, but under the political climate of today she seems to be okay.