Next to the candidates, there’s little doubt who will be the most important people at the upcoming presidential debates: the makeup artists.

For the first time ever, a sizable chunk of the audience may be watching the debates in high-def, which could expose every blemish, every wrinkle, every gray hair to a national audience.

“In every campaign, whatever frailties or flaws you have are going to become public,” says political strategist Chris Lehane. “Now whatever frailties or flaws you have physically are going to become public.”

In other words, you’d see even the salt-and-pepper strands emerging from Nixon’s 5 o’clock shadow if you were watching the famous Kennedy-Nixon debate in high-def.

In that first televised presidential debate in 1960, Nixon famously refused makeup while the more telegenic John Kennedy looked tanned and rested. The result was that radio listeners thought Nixon had won and TV viewers thought Kennedy had. Welcome to the television age.

With broadcasters and cablers planning to present this year’s presidential debates in HD, a similar transition is looming again. 

HDTV penetration is now around one third of the country by industry estimates — not earth-shattering but still significant.

“This is probably that transition election, maybe the last time that candidates don’t have to worry about their appearance in high-definition,” says Alan Schroeder, associate professor in the School of Journalism at Northeastern U. and author of “Presidential Debates: 40 Years of High Risk TV.” “My guess is there will be some concern, but not a huge concern.”

The first debate on Sept. 26 in Oxford, Miss. will be vastly different from the forums of the primary season. Facing off one-on-one, Barack Obama and John McCain will have no shortage of closeup screen time, their images and words played and replayed for days afterward. The same will hold true when Joseph Biden and Sarah Palin debate in St. Louison Oct. 2.

The risks of HD are McCain looking even older, or Biden’s hair looking thinner. On the other hand, Schroeder notes, Obama and Palin may benefit from letting a few gray hairs show, to buttress the experience argument. “Maybe looking a little older and having your wrinkles show is not such a bad thing,” Schroeder says.

Fred Davis, the veteran admaker who is a consultant to the McCain campaign, says the HD issue “hasn’t crossed our radar.”

It’s still early, as the campaigns hash out debate logisticson everything from the placement of dressing rooms to the distance between the podiums to the number of questions that will be asked by each moderator. The 32-page 2004 agreement between the John Kerry and George Bush campaigns, posted online, included such provisions as, “The chairs shall be swivel chairs that can be locked in place, and shall be of equal height.” Each candidate was allowed to bring his own makeup artist.

Therein lies the risk: A shoddy makeup job and you can look like Al Gore did at the first debate in 2000.

Lehane, who served as press secretary on his campaign, remembers watching in the basement of the gym at the U. of Massachusetts at Boston, wondering why his candidate had a strange, almost orange-ish, tint. “I just assumed it was the TV set,” he recalls.

It’s a reminder that as much as issues are talked about at debates, stagecraft matters too.

Each candidate faces perils. McCain looking too out of touch, Obama and Palin looking vulnerable on the experience issue and Biden coming across as anything close to sexist:

“All four of these folks are going to be on a bit of a high wire,” says Lehane.

With HD, it’ll be as if we’re all watching them under a microscope.