Of course they will. They might not love him but they will heavily support him against Trump. The excellent Perry Bacon Jr. explains why this is the reasonable expectation in a piece on 538. Bacon also addresses the turnout issue about which he sees more cause for concern. But even there, he reminds us that turnout of young voters is always relatively low, so the real question is whether their turnout will go down relative to other age groups. I rather doubt that myself; I expect 2020 to be a high turnout election in general and for young voter turnout to go up commensurate with trends among other age groups. That's what we saw in 2018 and it's likely what we'll see in 2020.
One of the defining features of the Democratic primary has been the age divide among voters — those 45 and over have overwhelmingly backed former Vice President Joe Biden, while those under 45 have generally supported Sen. Bernie Sanders. Now that Biden is the likely Democratic nominee, many political observers have started to wonder whether his lack of support among younger voters will be a problem for him against President Trump in the general election.
According to exit polls from recent elections and polling data from this year, the answer is, not necessarily.
First, Biden is likely to win voters under 45 by double digits against Trump. The former vice president would have two big advantages: He’s a Democrat, and he’s running against Trump. Democrats have won the under-45 vote in every recent election — even in cycles that were terrible to mediocre for the party overall, such as in 2010, 2014 and 2016.
Compared with other age groups, younger voters overall tend to hold more liberal views on social issues and the role of government. Furthermore, the cohort of Americans under 40 includes significantly more Asian, black and Latino people than the cohort over 40 — all Democratic-leaning groups. But even younger white people tend to vote for Democrats at higher rates than their older counterparts.
Hillary Clinton won the under-45 vote by 14 percentage points in the 2016 general election, according to exit polls, a margin similar to that won by then-President Barack Obama four years earlier.1 But in the 2018 midterms — essentially a referendum on Trump’s performance even though he wasn’t on the ballot — Democrats won voters under 45 by 25 points. These results in part were likely due to a backlash against Trump among younger voters, who disapprove of the president’s job performance much more so than do older voters.
This isn’t likely to change in 2020. Polls already show Biden with massive leads against Trump among younger age groups. And I would expect that margin to grow if the Democratic Party, including Sanders and his supporters, consolidates around the former vice president."