While Hillary Clinton's Iraq vote opened the door for a candidate who solidly opposed the war, it would be silly to ignore the value of the Obama campaign's comprehensive field work and ground strategy, which focused much of its organizing energy in small caucus states. Tom Schaller highlights this piece by Justin Sizemore which nicely synthesizes the strategy and details why it was so effective:

Caucuses let candidates achieve more bang for their organizing buck, and the Obama campaign would demonstrate that mobilizing a few thousand people in a caucus state can have as much impact as getting several hundred thousand voters to the polls in a primary state. Obama's young, affluent supporters and dedicated activist base gave him an inherent advantage in caucuses. But his overwhelming landslides in those contests were not inevitable: the Illinois senator invested considerable resources to build sophisticated grassroots mobilization efforts in states Hillary Clinton ignored.

The key turning point? Four post-Super Tuesday caucuses:

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 strengths, 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.