There was a time when Barack Obama disavowed his middle name, Hussein. During the 2008 campaign, Obama’s aides bristled even at references to him by his initials BHO, so sensitive were they to the offending “H.”

Then, after he won the election, he proudly brandished his middle name as evidence of his connection to the Muslim world and of America’s tolerant embrace of people with even the most exotic backgrounds. With new polls showing 18 percent (in a Pew Research poll) or 24 percent (in a Time magazine survey) believing Obama is a Muslim, the name Hussein is surely headed back to a secure, undisclosed location.

That a sliver of Americans believe Obama is a Muslim is not shocking in the context of other bizarre and stupid things they tell pollsters. In a rebuke to geography teachers everywhere, 10 percent of people either don’t think Hawaii is part of the United States or aren’t sure. Twenty percent believe aliens have contacted us here on Earth. And 11 percent have confidence in the United States Congress.

But the numbers tell us something important about Obama: We don’t know him. The most powerful and famous man in the country is still the mysterious stranger. He rose from nowhere, winning an election based partly on being an unknown quantity, and an unknown quantity he remains.

Obama has proven adept at crafting and then casting off synthetic identities. He was the good-government-process -obsessed reformer – until he wanted to raise countless millions of dollars outside the campaign-finance system. He was the post-partisan scourge of politics as usual – until his hyperpartisan first 18 months in office. He was the moderate – until he pushed his vast left-wing spending agenda.

Obama’s candidacy always had the sense about it of a supremely artful marketing campaign. His bio video during the Denver convention made him sound like a corn-fed product of the American heartland. There was barely a hint of the father from Kenya and the boyhood in Indonesia and Hawaii – in short, what made him so biographically alluring to worshipful journalists.

He was the blank canvas upon which people could paint their visions of grandeur. One moment Obama was the loyal parishioner of the Rev. Jeremiah Wright, who converted him to Christianity and was the fount of preacherly wisdom from whom Obama ripped off his most famous rhetorical riff, “the audacity of hope.” The next, he’d hardly heard of the good reverend.

An element of the Obama-is-a -Muslim opinion is perfervid critics wanting to believe the worst of him, but not all. According to Pew, the number of Americans who identify him as Christian has declined from 51 percent in October 2008 to just 34 percent. The more we see of him, the less we know of him. Only 46 percent of Democrats and 43 percent of blacks think Obama is a Christian. His faith simply hasn’t made an impression on the public.

Compared with his predecessors, Obama is as transparent as a billiard ball. You knew George W. Bush was an unapologetically pro-business, freedom-spreadin’ Texas evangelical. You knew Bill Clinton was a flawed but brilliant Southern operator, part of whose charm was the ability to lie with impressive fluidity. Who is Obama?

He’s a man constantly traveling under a cloak of ideological falsity, since he can’t speak frankly of his big-government ambitions. He’s emotionally remote. And he’s the product of life experiences alien even to his most natural supporters. In the heat of the controversy over her firing from the Agriculture Department, civil-rights activist Shirley Sherrod pointedly noted that Obama “is not someone who has experienced what I have experienced through life.”

None of this would matter particularly if Obama’s program were working – he could identify himself with its successes. As it is, he’s the cipher in chief, overexposed but underperforming, as detached as a law-school lecturer. Obama is assuredly not a Muslim. For many of his countrymen, though, he remains a question mark.