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Analysis: Which voters are changing their minds in fluid Democratic primary race?

Voters still not committed to one candidate

CBS News has been closely tracking the race for the Democratic presidential nomination since the summer, interviewing and reinterviewing thousands of voters across the early primary and caucus states. The data have shown an evolving race with Joe Biden leading initially but being eclipsed by Elizabeth Warren, who holds a lead among Democratic likely voters in the 18 states holding contests through Super Tuesday.

Kamala Harris, on the other hand, has dipped in our polling since her post-debate high over the summer. Other candidates have gained in particular states, as Pete Buttigieg has in Iowa recently. And in each wave of the CBS News/YouGov Battleground Tracker, most voters have told us they are considering multiple candidates.

A virtue of the Battleground Tracker is that we recontact respondents, allowing us to track how individual voters change their minds over the course of the campaign. This analysis includes 2,746 Democrats and Democratic leaning independents whom we surveyed in July, September, and October — three times total.

Overall, 4 in 10 Democratic likely voters have changed their minds about their first-choice candidate since July: 30% of voters switched in September, and 26% switched in October.

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Who's switching candidates?

One of the predictors of which voters switched candidates is their self-described ideological viewpoint. About 4 in 10 voters identifying as somewhat liberal or moderate switched — a higher rate than the 34% of very liberal voters who switched. (The latter have been favoring Warren and Bernie Sanders pretty consistently.) The smaller group of Democratic voters who identify as conservative were the most likely to switch: 62% have done so since July.

Another interesting difference occurs by race. White voters were slightly more likely to switch candidates than black voters were. The main beneficiary of black voters' relative consistency is Biden, who has held a strong lead with them in each wave of our polling. (Even though black Democrats are more likely than white Democrats to identify as moderate or conservative, the difference in switching rates by race holds even when controlling for voters' ideology.)

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One other difference in which voters are switching concerns what voters want to hear candidates talk about. In September, we asked voters what they would most like to see candidates talk about during the debates. 

Six in 10 said, "What they would do if they became president," while the rest split evenly between "How they are different from their Democratic opponents" and "Why they can beat Donald Trump." While only a third of those in the first group ("what they would do") have switched candidates at some point, nearly half have done so in the other two groups — which are more focused on the 2020 elections than what the nominee would do from the White House.

Who's lost (and won back) supporters?

The chart below shows how many of a candidate's July supporters switched at some point since then. Importantly, some voters switched candidates in September only to switch back to their initial candidate when we interviewed them a third time. Candidates who lose supporters don't always lose them for good.

For example, about 2 in 10 of Warren's July supporters changed their minds at some point (the lowest rate for any of the leading candidates). While 13% of her July supporters switched away from her and stuck with different candidates, 7% of them ended up switching back to her in October. So her net loss between July and October was really just 13%.

Sanders and Biden have lost a respective 18% and 23% of their July supporters, but Biden had more switch back to him in October, mitigating his losses (7% switched back vs. 3% for Sanders). A sizable 35% of Buttigieg's July supporters switched away from him, but another 11% switched back.

Harris has lost the biggest chunk of her July supporters: 65% switched away, while only 7% switched back to her. These voters changing their minds have driven her decline in the polls since the summer, with the plurality of them now backing Warren.

Of course, there's good reason to think some of these switchers will come back to these candidates, as some voters have in the past. We've already seen a fluid race, and with more than three months to go until the Iowa Caucuses, there is plenty of time for voters to keep changing their minds.

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