The second test for Carson is overcoming the implausibility of a brain surgeon’s becoming president. This won’t be easy. It may even be impossible. But it’s an obsession with Carson. He’s been insisting for years that nonpoliticians shouldn’t be ruled out for high office. “We need doctors, we need scientists, engineers,” he told the prayer breakfast. “We need all those people involved in government, not just lawyers.” In his book America the Beautiful, published in 2012, he said critics would discredit him by saying: “He is a brilliant surgeon, but he knows nothing about politics, law, and economics, and should confine his opinions to medicine.”

Carson stoutly defends a role for doctors in politics. Five signed the Declaration of Independence, he reminds audiences. Doctors are the “most highly educated group in the nation, trained to make decisions based on facts rather than emotion,” he wrote. “They tend to be excellent with numbers, very concerned about the welfare of others, and accustomed to hard work.” In the TV documentary, he carries the argument further. “One’s profession doesn’t dictate what one knows,” Carson said. “It dictates what one has to know to perform the duties of their profession. You don’t have to restrict yourself.” Also, “you have some people who are trained to be rational, and that helps when you throw them into the mix.”

For Carson, the campaign is the mix. The televised campaign debates with Republican candidates will be crucial. If he’s as credible and persuasive as Republican heavyweights like Bush and Romney, Carson’s reputation will soar. If he’s not, his campaign will be over. Campaign chief Terry Giles says the Carson operation will produce a series of policy papers. “He is looking to change the country. .  .  . We’ll actually have a plan .  .  . to move the country back to where it was.” For Carson’s sake, the plan better make sense.