After his wipeout Saturday in the Nevada caucuses, John Edwards was hoping, as he said gamely, “that what happens in Vegas stays in Vegas.”

Because simply put, Edwards flunked the viability test that is fundamental to remaining in the Democratic race. Viability means you need 15 percent of the votes to get a proportional share of the delegates; less than 15 percent, you get no delegates. On Saturday, entrance polls showed Edwards with 10 percent of the caucus-goers, but that only meant he wasn’t viable in most of the caucuses and his supporters weren’t counted. He ended up with 4 percentand no delegates.

Thus Edwards limps into this Saturday’s South Carolina primary, where polls show him running in the teens, far behind front-runners Barack Obama and Hillary Clinton. He’s in danger of falling below 15 percent there tooin his native state.

So is South Carolina Edwards’ last stand?

When I talked to Edwards’ longtime friend Gus Gusler Sunday, he didn’t think so. “I think if he can finish second or a close third, it’ll be a good result,” he said, adding, “I absolutely think John still has a chance to win the nomination.”

Gusler, a lawyer and owner of the venerable Players Retreat bar and restaurant near the N.C. State campus, has been friends with Edwards for 25 years. He pitched in on the campaign in Iowa for a week after Christmas, then flew on to New Hampshire. The night before the New Hampshire primary, he was backstage with Edwards’ former law partner David Kirby and another pal, Fayetteville attorney Wade Byrd. John and Elizabeth Edwards were both “cutting up” and in great spirits, he said, despite the fact that everyone there knew they were headed for a disappointing third-place finish.

“The way this whole thing is going, I don’t think anybody can predict what’s going to happen,” Gusler said. “It’s way too early to be talking about any of the top three dropping out.”

Maybe, but press pundits are talking about it. In fact, they’ve stopped ignoring Edwards and have started peppering his campaign with questions about when he’ll fold. “What’s Edwards’ ‘rationale’?” they’re asking.

The answer, Gusler thinks, is that 47 out of 50 states haven’t voted, and if Edwards starts to gainwell, Edwards is right around 15 percent in most of the national polls, so if he moves up, maybe Clinton and Obama both stall? And maybe Democrats start to consider Edwards’ argument about electability, which lately is about how he can defeat John McCain … and are you sure Clinton or Obama can?

But no need to listen to the talking heads about this. Edwards’ voters will decide it. As long as they think Edwards is representing them in the race and the other two candidates aren’t, Edwards will score above 15 percent and collect delegates to the Democratic convention. When they don’t, he’ll drop below 15 percent, and his viability will be what it was in Nevadazero.