Foxx's support is especially notable because it comes from a conservative base most likely to turn out in a primary election: among voters identifying as "very conservative," she holds a 20-point lead.

Hagan is seen as potentially vulnerable, and the PPP survey found her approval ratings underwater, with 41 percent approving of her handling of the job and 42 percent disapproving.

But Hagan still holds a lead against every potential Republican challenger, including a 46-39 percent lead over Foxx, a 44-40 percent lead over Berger and a 45-40 percent advantage over Tillis.

"Despite Hagan's lead over all the Republicans at this point the numbers certainly continue to point to a very close race," said PPP's Tom Jensen in a statement. "None of the GOP hopefuls have more than 50 percent name recognition, so there's a decent chance that as the eventual candidate becomes better known they will gain some ground."