This a theory we hear a lot about these days. The idea seems to be that Biden is such an awful and uninspiring candidate to young voters and Bernie supporters (mostly young) will be so aggrieved if Sanders fails to get the nomination--defecting in very large numbers by either voting for Trump, voting for some third party candidate or just staying home--that Biden will be sunk in the fall against Trump.
I am very skeptical of this theory. The emphasis on Sanders' enthusiasm advantage among the young ignores his enthusiasm deficit among older voters. And it is my suspicion that the Sanders supporters who are most vociferous about how they could never, ever vote for Biden may indeed be representative of diehard Bernie supporters on Twitter but perhaps not of the median Bernie supporter in the great wide world of American politics.
To test these ideas, I took advantage of the ongoing UCLA/Democracy Fund Voter Study Group Nationscape survey, which polls 6,000 respondents a week. Here is what I found.
In the latest wave of the survey (March 19-26), Biden is leading Trump by 8 points, while Sanders leads Trump by 3 points. Sanders does indeed lead Trump by more (5 margin points) than Biden does among young (18-29 year old) voters. But Biden leads Trump by much more (11 margin points) than Sanders does among the 65+ age group. In fact, Sanders flat out loses to Trump among this age group by 49-42. This has been a consistent pattern in Trump trial heat questions where Sanders loses more relative to Biden among older voters than he gains among younger voters.
With the survey, we can also look directly at Sanders supporters--those who voted and would vote for him a Democratic primary-- and see what choices they make in a Trump-Biden trial heat. I find that Sanders supporters would give Biden 78 percent support, 13 percent would vote for Trump and 9 percent say they don't know--presumably they would stay home or vote third party. This is not an exceptionally high defection rate--it's slightly higher than 2016, according to the Cooperative Congressional Election Study, but much lower than 2008 among Clinton supporters. It's also worth noting that even in a Trump-Sanders matchup, 8 percent of Sanders primary supporters say they would vote for Trump.
Most tellingly, the defection rate among Biden primary supporters--who are substantially more numerous--in a Trump-Sanders matchup is greater than for Sanders supporters in a Trump-Biden matchup. I find that 74 percent of Biden supporters would vote for Sanders, 16 percent would vote for Trump and 10 percent don't know. Thus a Sanders candidacy would clearly be a bad tradeoff for the Democrats in terms of defection problems.
Could Biden benefit from more enthusiasm among young voters?. Sure, but the situation now is far less catastrophic than many think and Sanders, in an overall political sense, is not an effective solution to the problem.