CHARLESTON, S.C. -- In the fall of 2007, Hillary Clinton held a 24-point lead over Barack Obama among black voters in a CNN national poll. By Jan. 18, 10 days after the New Hampshire primary, Obama was winning blacks by 28 points in the same poll, a 52-point swing.

This time around, Clinton again holds a commanding lead among black voters headed into Iowa. She boasts a roughly 45-point lead nationally, which her campaign refers to as a firewall.

The assumption fueling that fire is that Obama was able to win over the black vote because, put simply, he was black. If that's the case, the uber-white Vermonter Bernie Sanders isn't a serious threat to that firewall, and the Clinton camp can bank on a South Carolina victory no matter what happens in Iowa or New Hampshire.

But that strategy may rest on a misreading of why the black vote shifted so rapidly to Obama the last time around. Indeed, Obama was just as black in October, when black voters were backing Clinton, as he was in January, when the vote shifted his way.

What changed? His viability.

After Obama's resounding victory in Iowa, the perception of him changed. All of a sudden, black voters saw that Obama could actually win.

The connection between Obama and the black vote is obviously a unique one, but the phenomenon is universal: Voters prefer to back a winner, and candidates appear more attractive the more likely they are to win. The Iowa caucus may only be a venue for some 250,000 or so Iowans -- a minuscule fraction of the national voting population -- but the decisions those caucus-goers make can send a signal that reverberates far beyond the state.

If Bernie Sanders or Donald Trump comes out on top in Iowa, it will be the first time that millions of people waking up on Tuesday morning seriously think of those men as presidential material. (The shock to the global audience, particularly if Trump wins, will be off the scale.) If Obama's experience is any guide, winning Iowa could possibly unlock significant additional support.

The reality is, if Mrs. Clinton loses Iowa and New Hampshire, that could create new and real problems for her here. S.C. Rep. Jim Clyburn

For the American voter prior to 2008, the only thing harder than picturing a black man winning the White House might have been seeing a socialist occupying it. But if Sanders comes out on top in Iowa and follows it up with a win in New Hampshire, where he's well ahead, all of a sudden he becomes a viable candidate, and the firewall could be snuffed out.

"The reality is, if Mrs. Clinton loses Iowa and New Hampshire, that could create new and real problems for her here," said Jim Clyburn, a Democratic congressman and civil rights leader from South Carolina.

While many people reading this article have been deeply familiar with Sanders for years, many others are coming to the race for the first time, driven by the news of the caucus and the coming New Hampshire primary.

Up until recently, Sanders was still largely unknown in the black community. While 86 percent of black voters in a recent Gallup survey had a favorable opinion of Hillary Clinton, 43 said the same for Sanders. But only 14 percent had a negative opinion, meaning nearly half had no opinion at all.

Nate Cohn, writing in The New York Times, noticed this weekend that poor and working-class white voters have been shifting toward Sanders and away from Clinton, an unusual pattern in a Democratic primary. If whites who often vote for the more conservative Democrat were moving his way, Cohn wrote, "the assumption that Mrs. Clinton will easily maintain her strength among nonwhite voters may be shakier than once thought."

In early 2008, it was quickly being forgotten that Obama had ever been losing the black vote, and losing it badly. While memories were still fresh, I interviewed more than a dozen African-American leaders and activists about the shift in support from Clinton to Obama. The story never ran; my editor at the time at Politico argued the piece made Obama look too good and spiked it. Thanks to the endless memory of Gmail, I dug it up this week as both Sanders and Trump -- both candidates whom millions of people have trouble seeing in the White House -- flirt with coming victories in Iowa. Interviews done for that ill-fated story are being used to flesh out this one.

(The interviews also provide a fascinating window into the sense of optimism alive at the time around race relations. The same connection won't exist between Sanders, of course, and the black community. But as Clyburn noted, those voters will give Sanders a second look -- or a first one -- if he starts winning.)

Joe Madison, a D.C.-based talk radio host considered one of the most influential in the black community, recalled in 2008 that before Iowa, Obama wasn't treated as credibly by his show's listeners, who wondered if "he would be the token black in the debate."

"I hate to put it that way, but I'm certain that's how folks looked at it," he said.

That all changed the night Obama won Iowa. "When that group said, 'We think Obama would be a good president,' that ignited something that said to everyone in our community, 'We might have something here,'" said Rev. Kyev Tatum, then senior pastor at Servant House Baptist Church in Ft. Worth, Texas.

Iowa happened. The minute it became possible that he could be the nominee, he was going to win the lion's share of the African-American vote and I never begrudged it. Bill Clinton

Jamal Simmons is a Democratic consultant and a CNN contributor who also worked in the Clinton White House. Simmons, an Obama supporter, said he saw the 2008 shift in attitude in his own Detroit family, most of whom thought Obama had no shot with white America. "It is challenging the African-American community's assumptions of white people," he said.

For Madison's listeners, the ultimate moment of truth arrived when Obama won Idaho. "A black man won Idaho? I don't know if there's any whiter state in America than Idaho. That was the ... comical relief that sort of solidified it," Madison said. White America embracing Obama announced "a different era, that's the best way to put it. And that's what people said: 'We've moved beyond the Civil Rights era of segregation, Jim Crow. Racism exists; we know that it exists; but it is not all consuming.'"

Raynard Jackson, a black Republican campaign consultant and the host of an XM Satellite radio show, is a Virginia resident who crossed party lines to vote for Obama in the state primary, but was uncommitted in the general election. "If South Carolina had come before Iowa and New Hampshire, Obama wouldn't have won," he said in 2008. "After New Hampshire and Iowa, the whole tide turned and he became credible, not because black folks changed their minds, but it was more as a result of white America validating to the black community that, 'Hey, he's OK with us.'"

Former President Bill Clinton agreed with the analysis. In an interview that year with MTVu, he was asked what happened to the black vote. "Iowa happened. The minute it became possible that he could be the nominee, he was going to win the lion's share of the African-American vote, and I never begrudged it," he said. "You can't blame the African-American community for being proud of having a candidate who's immensely impressive and has had a lot of support in the North among non-African-Americans and has generated all this excitement among young people. I don't think it's rocket science."

Obama himself seemed to recognize the significance of the Iowa victory. "Years from now, you'll look back and you'll say that this was the moment. This was the place where America remembered what it means to hope," he said in his victory speech that night.

Obama consultant Cornell Belcher, the highest-ranking African-American pollster, picked up a similar thread at the time. "African-Americans are beginning to see and sense that, quite frankly, that they have a lot more in common with white voters than not," he said. "The eye-opening thing was to see that whites share the same sort of aspirations and same sort of anxiousness about what's going on in the country as African-Americans do."

Rep. Hank Johnson (D-Ga.) said in '08 that the early willingness of white voters to back Obama threw previous racial assumptions into doubt. "I do sense that people are aware of a thing that's occurring in this country, with white folks willing to have a black man represent them. It makes their eyes open wider," he said. "It does away with the 'blame game' and the 'race card' and all the previous ways we've had of explaining our station in life, if you will. All this is being obliterated right before our eyes. It's a clean break between the past and the future with an understanding that all of the problems in the world put us all together, regardless of color."

Obama's rise may have been more surprising to the black community than to anyone else, said several observers. "I didn't see it coming. A year ago there was no passion. A year ago it was a question of whether he was black enough," said Madison.

Eddie Griffin, who at the time was a Ft. Worth member of the AfroSpear, a group of black bloggers, said that the obliteration -- a word used independently by several observers -- Johnson spoke of was changing black attitudes towards mainstream America.

"I tell you it has changed our young people. Young people have a different swagger about themselves. The hip hop generation is cleaning it up, pulling their pants up. They're beginning to try to look respectable, more like Barack," said Griffin, an Obama backer. "I'm beginning to see that even on the streets here of Ft. Worth. My little gang bangers are beginning to have a different look about themselves. And volunteering! And volunteering in the campaign--passing out fliers, door-knocking."

On Sunday, Sanders announced that he had raised $20 million in January alone, nearly all of it from small donors.

Ahead of the Democratic primary debate in Charleston earlier this month, Clinton highlighted endorsements from high profile black leaders, like former Attorney General Eric Holder. More black Democratic state lawmakers have endorsed her than Sanders. But state Rep. Gilda Cobb-Hunter, a member of the Democratic National Committee, recalled what happened in 2008 to point out that Clinton's double-digit lead in South Carolina could erode.

"South Carolina's black vote is not a monolith," she said. "No one controls the black vote. What those of us who were here know is that in 2008, most if not all of the elected officials here were not with [Obama]. It was a grassroots movement that bypassed elected officials. There was nothing she or anyone else could have done to stop it. It was sheerly the force of nature."

In some parts of the country, the shift of black voters to the black candidate in 2008 felt less dramatic. "It's not new in Virginia," said Rep. Bobby Scott (D-Va.) at the time, adding that "we've been electing African-Americans to office for a long time." Political analyst David Bositis agreed that the shift was a matter of geography and experience. For black voters in states like South Carolina, he said, their "political experience [told] them that African-Americans cannot win support from whites."

Belcher wouldn't share Obama's internal polling when asked back in 2008, but survey timing supports the idea that Iowa triggered something in the black community. "If you look at Iowa as a key inflection point, that's the point at which African-Americans started supporting him with their vote," Doug Usher, director of research at Widmeyer Communications, said at the time.

Bob Friedman, a talk show host and operations manager at the oldest black-owned radio station in Alabama, said that he noticed the shift in listener attitudes after Iowa. "I remember a caller who called and said, 'In some ways the white vote sanctioned his identity as a new kind of black candidate, a black candidate with crossover appeal. The white community was kind of giving a heads up,'" said Friedman, who is white. Several observers emphasized that it was Obama's ability to raise money as well as get votes that persuaded the black community that he was for real.

On Sunday, Sanders announced that he had raised $20 million in January alone, nearly all of it from small donors. “The numbers we’ve seen since Jan. 1 put our campaign on pace to beat Secretary Clinton’s goal of $50 million in the first quarter of 2016,” Jeff Weaver, Sanders’ campaign manager, said in a statement. “Working Americans chipping in a few dollars each month are not only challenging but beating the greatest fundraising machine ever assembled.”

If that kind of financial strength can be coupled with a handful of victories, Sanders could very well blow right through the Clinton firewall.

Samantha Lachman contributed reporting from Charleston. Ryan Grim reported from Washington, D.C.

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