Tuesday night’s debate was the last one before the voting starts in Iowa, and before the debate, our forecast thought there was roughly a four-way tie for who will win the caucuses. So to get more insight into this neck and neck race, we once again partnered with Ipsos to track how the debate, hosted by CNN and the Des Moines Register, affected likely primary voters’ feelings about the candidates on the stage. The FiveThirtyEight/Ipsos poll, conducted using Ipsos’s KnowledgePanel, interviewed the same group of voters twice, once on either side of the debate, to capture both the “before” and “after” picture.

To better understand which candidates did well or poorly Tuesday night, we plotted how favorably respondents rated the candidates before the debate vs. how debate-watchers rated candidates’ performances afterward — and Elizabeth Warren, in particular, seemed to have a breakout evening according to this metric. She not only received the highest marks for her debate performance, but her scores were high even relative to her pre-debate favorability rating.

That said, Bernie Sanders, Pete Buttigieg and Joe Biden also received medium-to-high marks for their performances, but because of their relatively high pre-debate favorability ratings, we expected a lot of voters to already be predisposed to viewing their debate performances in a positive light. So while they still did pretty well on the debate stage, they didn’t exceed expectations the way Warren did. Amy Klobuchar and Tom Steyer, on the other hand, tied for the lowest overall debate grades, putting them only barely above where we’d expect them to be given their pre-debate favorability ratings.

The numbers behind the chart

Candidate Pre-debate favorability Debate performance Elizabeth Warren 65.9% 3.3 Bernie Sanders 68.2 3.1 Pete Buttigieg 60.3 3.0 Joe Biden 66.8 3.0 Amy Klobuchar 54.0 2.9 Tom Steyer 52.8 2.9

In terms of raw debate grades — respondents graded candidates on a four-point scale (higher scores are better) — Warren got the highest average score, closely followed by Sanders, Buttigeg and Biden.