This is the most thorough run-down I’ve seen of how Obama won the race. The turning point was the week after Super Tuesday:

On Wednesday, February 6, the race for the Democratic nomination was virtually tied. With more than half the pledged delegates spoken for, Barack Obama led Hillary Clinton by about thirty. In the next seven days, Obama would turn his slight lead into an insurmountable one.

On the weekend after Super Tuesday, Maine, Nebraska, Washington State, and the Virgin Islands held caucuses to award a combined 129 delegates. (Louisiana, in which Obama was heavily favored, allocated its fifty-six delegates in a primary that Saturday .)

After seeing what had happened in the February 5 caucuses, the Clinton campaign undoubtedly knew what was coming and went into triage mode, flying twenty-two operatives into Seattle the day after Super Tuesday.

“It’s a huge shot in the arm,” remarked the director of Clinton’s previously all-volunteer Washington effort. The caucuses were three days away.

Despite the Clinton campaign’s last-minute organizational surge, Barack Obama successfully applied his Super Tuesday blueprint the following weekend. But there was one crucial difference: without any states in which Clinton could offset Obama’s streng ths, he was able to translate his advantages into a massive gain in delegates. Together, those five jurisdictions gave Obama a net gain of fifty-five delegates.