The breadth of Barack Obama's electoral appeal has shifted over recent weeks. In South Carolina his support among African Americans and the young has grown, while backing from the young and women has fallen.

But the depth of his support has never really been questioned. Obama, we've been told, is a different kind of candidate. His supporters don't just like him; they love him. They won't walk to the polls to vote for him, they will run. Since shortly before he announced his bid for the presidency a year ago, Obamamania, has gripped the nation.

For the Illinois senator to have a mania named after him is quite something. Reagan, Clinton and Kennedy were all very popular - but none could claim a mania. Strolling through Charleston during the Martin Luther King day parade on Monday, you did get a sense of something special.

His overwhelmingly white group of volunteers marched through black neighbourhoods cheering, dancing and waving, calling on the African Americans who lined the sidewalk to support them. African Americans clapped and cheered back. These are not scenes one witnesses often in the South. But when we tried to speak to them afterwards they told us they couldn't speak without prior permission.

"I just want to ask you why you're so excited about Obama?" I said. "Sorry, you have to call Columbia [Obama's South Carolina campaign office]," they reply.

It is so sad and pathetic when people lose their own voice. If one were in any doubt about whether this is a grass roots movement or a professional campaign, this kind of behaviour seems to settle it. A helpful staffer found a superior to give the go-ahead over the phone. The volunteers had all travelled huge distances, one from Guatemala, to be part of something big. One spoke of a post-racial America. All of them were excited.

The next day, in Sumter, we went to see how this excitement works when he is actually present. It was an interesting crowd. Sumter is roughly 50/50 black and white. The crowd was 98% white. The polls suggest an Obama win. But for all the talk about him taking the black vote, it could be a recalcitrant white vote that scuppers his chances.

Here the crowd was enthusiastic, but not impassioned. Most of the time he spoke they remained on their feet. Obama is by far the best speaker of all the candidates. But when it comes to oratory you can't help comparing him to Jesse Jackson (particularly in South Carolina), and he always comes up short.

He left with the crowd satisfied but not particularly wanting more. I asked one woman, who had led the crowd in chants, if she were an Obamamaniac. "I'm no maniac of any kind," she said. Have you seen much evidence of Obamamania? "No. People are excited. They want him to win. But that's it."

Once all is said and done, that should be good enough for Saturday.