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UPDATED Jan. 15, 2020, at 1:20 PM

Who Won The January Democratic Debate?

We partnered with Ipsos to poll voters before and after the candidates took the stage.

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.

Who won the debate?

The over- (and under-) performers

How favorably all likely primary voters felt about each candidate before the debate vs. how well respondents who watched the debate thought each candidate did

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

CandidatePre-debate favorabilityDebate performance
Elizabeth Warren65.9%3.3
Bernie Sanders68.23.1
Pete Buttigieg60.33.0
Joe Biden66.83.0
Amy Klobuchar54.02.9
Tom Steyer52.82.9

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.

How the race changed

Who gained (and lost) support

Share of respondents who are considering voting for each candidate

Before debateAfter debate

Respondents could pick multiple candidates or ‘someone else.’

Unsurprisingly, given her strong debate performance, Warren was also the biggest winner in terms of attracting potential voters. She gained a little over 3 points in the share of respondents who said they were considering voting for her. Buttigieg and Klobuchar also gained roughly 2 points each in potential support. Gains were pretty small for the other candidates, though — less than a point each for Biden and Sanders, and a little over 1 point for Steyer.

The popularity contest

Candidates' favorable and unfavorable ratings among likely primary voters

Before debate
After debate

We also asked likely Democratic primary voters how favorably they felt about each candidate both before and after the debate. And perhaps unsurprisingly, it was the less-well-known candidates who gained the most: Klobuchar and Steyer saw the largest jumps in net favorability (favorable rating minus unfavorable rating) — 5.8 points and 5 points, respectively. Buttigieg and Warren also did well on this metric, however, with Buttigieg picking up 4.7 points and Warren 3.9 points. Sanders and Biden’s net favorability, on the other hand, actually fell a bit — Biden’s dropped by 1.6 points, and Sanders took the biggest hit in this metric, falling by 3.6 points.

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Which matters most: policy positions … or winning?

Share of likely primary voters by whether, if they had to choose, they’d prefer a candidate who has a good chance of beating Trump or a candidate who agrees with them on the issues

Excludes respondents who chose ‘I don't know enough to say.’

Voters were also asked what matters more to them — a candidate who agrees with them on most issues or someone who would have a good chance of defeating President Trump — and as you can see, there was no change in these numbers. Democratic primary voters really want a candidate who can beat Trump.

Who voters think can beat Trump

Respondents’ estimates of the likelihood, from 0 percent (impossible) to 100 percent (certain), that each candidate would beat Trump if they were the Democratic nominee

Joe Biden
Bernie Sanders
Elizabeth Warren
Pete Buttigieg
Amy Klobuchar
Tom Steyer

Finally, we asked respondents to estimate each Democrat’s chances of defeating Trump, from 0 percent (no chance) to 100 percent (certain to win). Going into the debate, as in other general-election polls, Biden was the candidate voters thought was most likely to beat Trump, on average. He still leads on that question after Tuesday’s debate, with Sanders in second. But, as you can see below, Biden’s average stayed essentially unchanged while all the other candidates gained ground.

Respondents’ average rating of candidates’ chances vs. Trump

CandidatePre-debate averagePost-debate averageDiff.
Amy Klobuchar32.835.5+2.7
Elizabeth Warren51.954.5+2.6
Tom Steyer32.835.1+2.3
Pete Buttigieg42.744.2+1.5
Bernie Sanders58.859.6+0.8
Joe Biden66.466.2-0.2