I was kind of amazed to see Richard Burr declare upon filing that he had nothing to worry about in the primary because it is 'impossible for any candidate to get to the right of me.'
Although this is not the angle either of his primary opponents is working, his vulnerability within the Republican Party is actually on the moderate wing. While only 13% of conservative Republicans disapprove of him 28% of moderate ones do.
Those conservative Republicans who don't like him still support Burr by a 49-3 margin over a generic Democratic opponent. But the moderate ones who don't like him say they'll go Democratic by a 47-30 margin...and they probably won't be won over by his declarations that he's as far right as possible.
Burr's in a solid position right now because he trails by only 14 points among moderates, where Elizabeth Dole lost by 31 with them a year ago. This kind of rhetoric isn't particularly smart if he wants to do well with the 56% of North Carolina voters who aren't conservatives.
It may be that in this political climate Burr can do whatever he wants and still get reelected. But failing to show up for a vote on the jobs bill the day he filed and making grand declarations about how far to the right he leans aren't terribly savvy things to do to kick off your campaign, especially when your approval is in the mid-30s to begin with.