Republican presidential candidate Ben Carson talks to reporters Oct. 16 in Alexandria, Va. (Win McNamee/Getty Images)

Ben Carson, whose appeal as a political novice has thrust him to the top of the Republican presidential field, faces a critical test in Wednesday night’s debate — defending a policy platform that he is building so fast that he and his staff have struggled to explain it.

Carson, for instance, has indicated that he wants to loosen U.S. gun laws significantly. But his campaign says he doesn’t. Carson also said he wants to tax everyone at 10 percent, a system he said was drawn from the Bible. But Carson’s campaign says it could be 15 percent, or some other amount. Aides say to expect detailed plans in a month.

Wednesday’s GOP debate in Boulder, Colo., will bring 10 Republican contenders together at a crucial moment in an unusual race. Two outsiders, the retired neurosurgeon Carson and real estate mogul Donald Trump, have dominated a crowded field of well-known senators and governors. Carson in recent days has overtaken Trump in some early-state and national polls, and the two have begun to take swipes at each other.

To prepare for Wednesday night’s debate, Carson, who was a quiet and almost passive presence in the first two GOP encounters, showed his trademark combination of confidence and unconventional tactics.

He did not have aides pepper him with the kind of ­pre-researched, detail-oriented questions that the CNBC moderators might ask. Carson instead spent 12 hours Monday talking to about 15 regular voters.

Ben Carson has placed first in a national Republican presidential primary poll, pushing Donald Trump into second place for the first time since June. (Reuters)

They were pre-selected from attendees at Carson’s campaign events. And they asked whatever came to their minds.

“There is no question that will be asked at the debate that they haven’t asked and no concern he has not thought about,” said Armstrong Williams, an adviser to the candidate. “No one should be able to stump him.”

When the main debate begins at 8 p.m. Eastern time Wednesday, Carson will not be standing at the front-runner’s center lectern. That honor will still go to Trump, who has led the GOP field for months — and still did when the podium order was set last week. But then a national poll of Republicans released Tuesday by the New York Times and CBS News showed Carson narrowly leading Trump, 26 percent to 22 percent, within the poll’s six-point margin of error.

And in this race, leading means being attacked.

“We’ve got one person saying we ought to have a 10 percent flat tax that will drive up the deficit in this country by trillions of dollars,” Ohio Gov. John Kasich (R) said Tuesday in Ohio, criticizing Carson’s idea as one of a number of proposals from other candidates that Kasich, who is also running for the GOP nomination, described as unrealistic. Kasich continued, mockingly: “Why don’t we have no taxes? Just get rid of them all, and then a chicken in every pot on top of it.”

Carson’s advisers say that the debate stage is a new environment for him, different from the thousands of stages he has visited as a motivational speaker, telling the story of his rise from poverty to pioneering surgeon.

Most important, they say, Carson needs to be more succinct and direct in his answers.

“I tell him not to be too overly intellectual,” Williams said. “His mind goes so fast that sometimes his ideas are traveling at the speed of lightning when we are all listening at the speed of sound. So the challenge is to be able to explain what you believe clearly.”

In the past few days, as Carson, 64, has crept up in the polls, he has begun to face tougher questions about his policy ideas.

In some cases, he struggled to explain exactly how they worked.

This past Sunday, on NBC’s “Meet the Press,” Carson was challenged on his statements that the Second Amendment was intended to make sure Americans had the weapons they needed to fight back if their government turned tyrannical. The implication was that the weapons available to citizens ought to keep up with the weapons possessed by the government so the fight would be even.

“The principle was that the citizenry should have access to whatever they needed in order to protect themselves from an overly aggressive government,” Carson said.

The show’s host, Chuck Todd, asked where Carson would draw the line.

“I mean, should somebody be able to have one of these surface-to-air missiles?” Todd said.

“I don’t think you can get a surface-to-air missile legally in this country,” Carson said.

In a phone interview Tuesday, however, Carson spokesman Doug Watts said that — despite Carson’s comments on “Meet the Press” — the candidate does not want to change gun laws.

“Whatever is available and legal today, he believes should be available and legal,” Watts said.

Carson’s plan for income taxes — the one Kasich attacked Tuesday — also seems incomplete.

Its essence is that everyone, even the very poor, should pay something in taxes. As Carson has explained it, they should pay the same rate as the very rich.

“The one that I’ve advocated is based on tithing, because I think God is a pretty fair guy,” Carson said at the first Republican debate. “And He said, you know, if you give me a tithe, it doesn’t matter how much you make. If you’ve had a bumper crop, you don’t owe me triple tithes.”

If Carson tried to pass such a plan as president, it would carry significant political risks. For one thing, it would serve to raise taxes on the poor — about 45 percent of Americans pay no federal income taxes at all now, and many would pay something under Carson’s plan. Also, a 10 percent rate would bring a major tax cut for the rich — and lead to a significant decline in the federal government’s revenue.

It also isn’t, strictly speaking, how the system in the Bible worked, according to theologians.

“Number one, it was not 10 percent,” said Andreas Köstenberger, a professor of theology at Southeastern Baptist Theological Seminary in Wake Forest, N.C. Köstenberger said that the original tithe, practiced by ancient Israelites, added up to at least 20 percent. “Number two, it was not just money,” Kostenberger said, but included other assets such as cattle.

Watts, Carson’s campaign spokesman, said that Carson would settle on the details of his tax plan — including the flat rate that everyone would pay — within a month. He said Carson would also release details of his plans to overhaul health insurance, including Medicare, within 30 days.

On illegal immigration, Carson has released some details of his plan, but he has left key parts murky.

He has said, for instance, that he does not want to follow Trump’s model and deport the approximately 11 million undocumented immigrants in the United States. Instead, Carson said, he would give those 11 million people six months to apply for “guest worker” status, meaning that they could live and work legally in the country but could never become citizens.

When Carson sketched out this idea last year in a newspaper column reprinted in his book “What I Believe,” he said that the immigrants would not be able to apply from within the United States. “People already here illegally could apply for guest-worker status from outside of the country, meaning they would have to leave first,” Carson wrote.

But his mind has changed. Watts said Tuesday that Carson no longer wanted to make the immigrants return home first. Carson also has not laid out a plan for another key contingency: What would he do with the immigrants who choose not to take the risk of applying for guest-worker status?

“I don’t think he’s thought through enough what’s involved here,” said Mark Krikorian of the Center for Immigration Studies, which favors reduced immigration. “When you’re in that situation, you end up stepping on a rake and hitting yourself in the face, like in the cartoons, because you don’t know where the rakes are.”

Another possible trouble spot: If Carson creates a class of guest workers, what about the children born to those workers? Would they be granted citizenship, as the U.S.-born children of undocumented immigrants are today?

“He is leaning against that,” Watts said. “I’m not giving that to you as a hard-and-fast position.”