Graham's approval rating with primary voters is at 66 percent, with 26 percent disapproving. He leads a generic "more conservative" Republican in the race by 51 to 40 percent, a big jump from the 37 to 52 percent position he was in when the pollster last checked slightly less than a year ago.

Graham's standing jumps when paired against actual Republicans who could theoretically challenge him. He leads Rep. Tim ScottTim ScottIs Senate ObamaCare repeal bill too mean? The Hill's Whip List: GOP undecided, 'no' votes pile up on ObamaCare repeal bill Lawmakers celebrate National Selfie Day on Twitter MORE (R-S.C.), who may be picked to replace retiring Sen. Jim DeMint (R-S.C.), by 54 to 32 percent. He has a 57 to 29 percent edge over Rep. Trey GowdyTrey GowdyInvestigation shows DHS did not hack Georgia computers It's time for Republicans to play offense while Democrats are weak Gowdy won't use Oversight gavel to probe Russia MORE (R-S.C.), a 64 to 26 percent edge over former South Carolina Gov. Mark Sanford (R), a 64 to 20 percent edge over Rep. Mick Mulvaney (R-S.C.) and a 67 to 17 percent lead over state Sen. Tom Davis (R), who many have speculated will challenge Graham but recently told The Hill that he "probably" won't run for the seat.

While many Washington-based conservative groups want to see Graham challenged in the primary, these numbers (along with the possible chance to run for DeMint's seat) hint at why no one has yet signaled they will run against Graham.

The poll of 506 Republican primary voters was conducted from Dec. 7-9 and has a margin of error of plus or minus 4.4 percentage points.