Going into the contest, the race had looked like a face-off between moderate Joe Biden and progressive Senator Bernie Sanders. It could return to that beat, but for now Iowans have widened the road.
They have given a significant boost to Pete Buttigieg; left Biden scrambling to cook up a revival; consolidated Sanders' position as the leading liberal and kept senators Elizabeth Warren and Amy Klobuchar bubbling along for now.
Buttigieg and Sanders split the bragging rights. Buttigieg over-performed his polling and got a New Hampshire bounce. He is now level-pegging with Sanders there, but will need to prove he can draw African American support in more diverse states.
Buttigieg understands the importance of offering a positive vision and tone as an antidote to Trump. He spoke of the day the "sun will come up over New Hampshire" when Trump will no longer be president — an echo of Ronald Reagan's famous "morning in America" line. Biden has attacked Buttigieg's limited political experience.
Biden was second favourite going into Iowa in polling but finished fourth. His electability argument has taken a hit, and his ability to raise enough funds and stir enough grassroots enthusiasm is in doubt.
There are two plot strands to watch: Buttigieg's struggle with Sanders in New Hampshire and the intensifying fight in the background to be the moderate flag-bearer. What shape will Biden's campaign be in by the South Carolina primary? And will black voters stick with him?
If Buttigieg still doesn't appeal as a winner to more minority voters by then, Klobuchar, eye-catching in the debates, might. Warren, third in Iowa, seems most in danger of slipping as Buttigieg and Sanders dominate. Then there's Mike Bloomberg. The world's ninth-richest person would appear a tough sell to progressives. Yet he could get a fresh appraisal when the goal is to beat Trump.
Sanders is well-funded, well-organised, and gradually accumulating delegates. In a fractured field, he could end up the last candidate standing.
