We already know that Barack Obama won South Carolina on Saturday by a huge margin. Duh.

The outcome may be no surprise to those of you following Yahoo's Political Dashboard, who would have have seen Barack Obama dominate online buzz in the run-up to the South Carolina primary. But what explains Obama's skyrocketing numbers and Hillary's dip on the day of the primary?

I've been paying close attention to Yahoo! Buzz trends in the primary and caucus states, and have seen how the outcomes of those races are often closely reflected in the online attention paid to the candidates.

South Carolina was no exception. Obama experienced a spike in attention the day before the primary, while Hillary Clinton buzz went south, and Obama was consistently ahead of Hillary every day except January 22, the day following the CNN debate in South Carolina.

Meanwhile, John Edwards steadily kept to third place; like Hillary he dipped slightly on the day of the primary while Obama sky-ba-rocketed.

What does it all mean? We're not sure yet. But looking back at these numbers, it's clear that Obama had some serious O-mentum going into South Carolina (hat tip: Mike Turk). That energy hit a fever pitch on the day of the primary, augmented by Hillary's sinking numbers. What happened to SC voters on that day that 1) convinced them that Barack was their guy, and 2) caused them to lose interest in Hillary?

By the way, the stats are about the same for women voters, except there's an even greater gulf between Obama and Clinton: