In the latest Rasmussen Research survey of North Carolina voters, Richard Burr leads Elaine Marshall by 47-37.  From today?s release:

Any incumbent who polls below 50% at this point in an election cycle is
considered potentially vulnerable. It is striking to note that Burr
remains below that 50% mark in a political environment that is very
favorable for Republicans. If the political environment improves for
Democrats between now and November, the incumbent could be facing a
serious challenge. No incumbent has been reelected to the seat Burr
holds since 1968.

The first-term Republican senator barely reaches the
50% mark in a match-up against former state Senator Cal Cunnignham. In
that race, it?s Burr at 50% and Cunningham at 34%. Given that match-up,
five percent (5%) like another candidate, and 11% are undecided.