WHEN AN ENDORSEMENT BACKFIRES…. The conventional wisdom suggests Republican candidates, especially those in Republican primaries, are anxious to get an endorsement from former half-term Gov. Sarah Palin (R).

There are, however, exceptions.

A new Public Policy Polling survey in New Hampshire finds Kelly Ayotte’s (R) appeal to moderate voters crumbled in the wake of her endorsement by Sarah Palin and her lead over Paul Hodes (D) in the U.S. Senate race has shrunk to its lowest level yet, 45% to 42%.

Key finding: “Most of the movement both in feelings about Ayotte and in the horse race has come with moderate voters. Moderates make up the largest bloc of the New Hampshire electorate at 47%, and Hodes’ lead with them has expanded from just 8 points at 47% to 39% in April to now 21 points at 51% to 30%. Ayotte’s favorability with them has gone from +5 at 32% to 27% to -19 at 27% to 46%.”

To be sure, it’s just one poll, so I don’t want to overstate matters. But this nevertheless offers some evidence to bolster other recent polls that show a great deal of hostility for the right-wing Alaskan from everyone who isn’t part of the far-right Republican base.

In the case of the PPP survey, it’s pretty dramatic — Ayotte was faring well among moderate voters, and now she’s not. The only thing that’s changed of late is the endorsement, which New Hampshire Democrats were anxious to tout among in-state reporters.

Indeed, there’s a great irony here. For quite a while, Granite State Dems were anxious to tie Ayotte to Palin, noting the similarities between them (most notably, the fact that both quit their jobs, mid-term, to pursue grander ambitions). The charges didn’t really connect in New Hampshire — until Ayotte went ahead and accepted an endorsement from the conspicuously unintelligent Fox News personality.

Overall, Ayotte’s lead over Rep. Paul Hodes has dropped from seven points to three fairly quickly. This is currently a Republican seat — held by the retiring Judd Gregg — and Democrats have long hoped to turn it into a pick-up opportunity.

Thanks to Palin, that opportunity is suddenly looking more achievable.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.