This strikes me as a sensible analysis, from a reader in the Granite State:

As an avid conservative radio listener, NRO reader and NH resident, I’d like to offer some insight into Ovide’s surge. There are two major factors and I don’t think the Judicial Crisis Network radio buy was either of them (I’d never even heard or heard of it until your post @ NRO).
Both factors are reputation. Ayotte was the presumptive favorite and establishment pick, she carried outgoing senator Gregg’s endorsement (which can be a two edged sword, as he was known as the less conservative of the two when it was he and John the Younger Sununu as our Senate pairing), however she had also been appointed AG by tarnished Republican Governor and a Democratic Governor, so her rep was placed towards the center; there was then a significant and off-putting row between her and Bill Binney (who was a Johnny-come-lately rino in conservative clothing whose signature issue was that English should be our national language, which is an interesting hill to make your stand upon in the current political climate – really? not jobs? deficits? wars? spending? english? really?). They beat the hell out of each other and while Ayotte came out looking the better, she was tarnished by the fight in general and by having to campaign negatively.
The other factor that has made this election close is that Ovide has a stellar reputation in NH – he’s known as a really nice, good guy and he’s been around for a long time, and not just in politics. He made a from-out-of-nowhere run to win the Republican nomination for Governor over the presumptive favorite in 1996, but was also the chairman of the board for Ste. Marie’s Bank (a local credit union that claims to be the nation’s first) and his family have been prominent in the community for a long time. As a member of a politically active family in the NH1 race told me, “Everybody knows Ovide. Everybody loves Ovide.”
So you had the tarnishing of Ayotte by Binney, who made himself out to be the bad guy, and Ovide as the sensible, staying-out-of-the-fight, DeMint-endorsed conservative.