So let's take a look, statistically!
Setting aside all preconceived notions about who should have or could have or might have known, as far as I can tell the number of people who absolutely had to be in on the conspiracy at the time is three:
1. Sarah Palin, because she was either pregnant or was not.
2. Cathy Baldwin-Johnson, Palin's doctor, who either delivered Trig at the time and place claimed or did not.
3. Todd Palin, because he likely saw Palin's belly during the seven months she claimed to have been hiding her pregnancy from the public. Even if he did not, he traveled with Palin to Dallas and back while she says she was in labor.
(I'll explain below why no one else logically must have been in on it. But first let's look at these three through the lens of the article Sullivan posted.)
According to this thought-provoking formula, there is an average six percent chance that each conspirator will not fail due to disloyalty or incompetence. (Very easy to see why this makes the chance of success of most conspiracies infinitesimally small.) The formula assumes the conspirators have some incentive - financial or otherwise - to break their silence.
So let's look at this case. Do the odds hold up?
Sarah Palin has zero incentive to tell the truth. Her political identity is tied to being, by choice, the mother of a child with special needs, and she has greatly benefitted politically and financially from this identity. (Some argue that the child with Down syndrome was the clincher for Steve Schmidt in convincing McCain to choose Palin in order to shore up the support of the Republican base.) To reveal she had lied about this defining life event - and wiped tears from her eyes in front of Right to Life groups recalling it - would be political suicide. I would say there is nearly a 100% probability Palin will never willingly confess.
Cathy Baldwin-Johnson - Despite the fact that Palin secured several high profile awards and appointments for her, I cannot see why a respected doctor would have intentionally staked her professional reputation on a hoax, except that as the founder of A Children's Place for abused teens she may have initially become involved from a desire to help a teenager - perhaps Bristol - in trouble. I suspect she was as shocked as anyone when Palin suddenly announced she was seven months pregnant. However, when Palin claimed to reporters that her doctor had advised her to travel for thirteen hours by plane while leaking amniotic fluid, Cathy Baldwin-Johnson joined John McCain and the citizens of Alaska as victims of Palin's propensity for unexpectedly "going rogue." At that point, the doctor was forced to either publicly call the Governor a liar or to admit to malpractice-worthy behavior. Dr. Baldwin-Johnson spoke to a reporter with an attorney present and said only that it was "not unreasonable for her to fly back." Since that time she has refused all interviews and, two months later, rescinded her privileges at the hospital where the delivery supposedly took place.
Regardless of the reason for or degree of her involvement, Dr. Baldwin-Johnson has what might be called a professional imperative to keep the secret, and cannot be legally compelled to speak because she is protected by HIPAA. Like Palin, I put Baldwin-Johnson at close to 100%, as she will likely lose her medical license if the truth is revealed.
Todd Palin - though there have been many rumors of marital discord between the Palins, so far Todd has remained resolutely loyal to the Palin brand. Considering the non-anonymous revelations in McGinnis' book, if anyone ever cracked I would think it would be Todd. But so far the personal and financial benefit has remained high enough not to. Regardless, Todd is protected by the spousal privilege, so unless he decides he's had enough, he can't be compelled to rat. How much can one man take? I give Todd odds of 50/50. We shall see.
Okay, so back to the formula. According to my math, there is about a 17% chance that one of the conspirators will cause failure, or an 83% chance it will succeed. I'd call those odds pretty good for the conspiracy. Add to it a media completely unwilling to look critically at Palin's tall tale, and the odds improve even more.
Still, people ask, "How could no one have talked all these years?"
Well, who exactly would be doing the talking? Just for fun, let's look at everyone else. Forget, please, what would usually happen in most families. Let's just look at what is possible.
The kids. According to Palin herself, Sarah Palin's children were in the dark about the pregnancy for seven months. Setting aside the likelihood that not one of her kids saw her belly in a nightgown ever during those seven months, this shows that a secret of the magnitude of a pregnancy (or lack thereof) is possible in this family.
If Bristol is indeed the mother of Trig, it's even possible she is not in on the conspiracy. She could have given a premature child up for adoption in early 2008, and it could have been in an NICU or foster care until Palin presented it.
Palin's parents. Both Chuck and Sallie are on record as saying they never know what Sarah is up to and anyway, according to Palin, she did not tell her parents she was pregnant. She claims she also did not tell her siblings. So she could easily have not told them she was not pregnant.
Palin's staff. It's hard to believe not one of them would have noticed her pregnancy at the time (regardless of who may now say that they totally knew). Palin's staff handled her entire life - from coffee to per diems for her children to jogging strollers for photo shoots. But there is not one calendar entry for a prenatal appointment and not one email demonstrating a visit to Dr. Baldwin Johnson in the emails that have been released. There is no reason to believe any of her staff was in the loop.
The Johnstons. Whether or not Levi, his sister or his mom were aware of any Bristol pregnancy, there is no reason to think they would have been privy to Sarah Palin's plans, especially if even Bristol was not.
The staff at Mat-Su Regional Medical Center. How could an entire hospital be hoaxed? That is a very good question, and there is an excellent discussion of it here. I won't repeat it, but under very specific circumstances in a small rural hospital it is possible. Regardless, any paperwork relating to the birth - or lack of paperwork if there was none - is protected by HIPAA.
More to the point: if the pregnancy is as Palin described - pre-term, premature rupture of membranes, fetus with Down Syndrome and a hole in his heart, mother of advanced age with a history of miscarriage - how is it possible at all that the baby was admitted to Mat-Su, a facility that is not licensed for twin births? Add to this that Palin says that when she arrived labor was induced, and there is zero chance that if she walked in the front door she would not have been immediately transported to the NICU at Providence Regional Medical Center. There is no chance that the admitting nurse would have jeopardized his or her job by violating the hospital's license.
However, if there are Palins walking the halls with a baby at 7:00 in the morning just after shift change, and Palin's personal physician (who is on staff and a member of the hospital's board) says the baby was delivered during the night and the Governor of Alaska is not to be disturbed in room 11A, would the clerk at the front desk or the nurses who just came on shift have any reason to question it? Further, the baby Sarah's parents showed to KTUU on April 18th is a bruiser. Premature? Hole in his heart? Jaundice? Those conditions would have required extra staff attention. No way would an infant with those symptoms be allowed to be passed around the hallways by relatives and the patient's daughter's boyfriend. The staff at Mat-Su could not have been aware of the conditions Sarah Palin claims her child to have had.
Everybody else: If it's possible - and I believe I've shown it is - that Palin managed to keep her secret from her children, her parents, her staff and the employees of Mat-Su, how likely is it that anyone outside that crucial circle would be any wiser?
So! What I think we have here, is the exception that proves the rule.