As the former vice president shifts his focus toward the general election, one of the most important questions facing his campaign is whether he can fortify his tentative standing among younger voters without weakening his sturdy position among the old.

With several polls this month showing his support lagging among the youngest voters, a coalition of groups representing young liberals recently wrote Biden to warn he will struggle to mobilize the emerging generations in November unless he endorses more of "the bold ideas that have galvanized our generation," including many liberal priorities proposed by Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts during their losing primary campaigns.

But the same surveys almost all show Biden running better than any recent Democratic nominee among seniors, who have drifted toward the GOP over the past two decades. And tilting left on questions such as immigration and health care in an effort to excite more young voters could risk alienating some of the seniors who now see Biden as a reassuring alternative to Donald Trump's volatile and belligerent presidency.

"You can't really appeal to both" young and old equally, says Patrick Ruffini, a Republican consultant who recently published an analysis of the generational implications of a contest between Biden and Trump. "You've got to pick one and there's going to be a trade-off."

Most attention among Democrats has focused on the warning signs that Biden could face some of the same problems among young voters as Hillary Clinton did in 2016 -- not so much a willingness to vote for Trump but rather a receptivity to considering third-party options and especially a reluctance to vote at all.

"My memo to the Biden campaign is they can't mess around with this, they have to take it very seriously and they've got to make a concerted effort," says Ben Tulchin, the pollster for Sanders' campaign.

But some Democrats are also warning that as Biden looks to expand his reach among the young, he can't ignore the risk of surrendering his gains among the old. "It's a relatively easy political equation here: If you are going to trade older folks for younger folks, older folks do turn out at much higher rates," says Sean McElwee, co-founder and executive director of Data for Progress, a Democratic research firm that advocates for progressive positions.

Adds Ruffini, the GOP strategist: "It's not a popular answer to give, [but] if it comes down to a trade-off between overperforming among older voters and overperforming among younger voters, you'd still want to take the older voters. There are more of them; they vote."

The sweet spot for Biden is finding issues and a message that connect with both ends of the age spectrum. But that was a challenge that almost completely stumped him during the Democratic primary, when he survived crushing deficits among the young only through preponderant support among the old

Biden's primary support thin among young

A new CNN analysis of the combined results from all the exit, entrance and phone polls in 23 states during the 2020 Democratic nominating contest show Biden attracted only anemic support from young people across racial, gender and educational lines.

Overall, he carried just 16% of Democratic primary voters under 30, far behind Sanders' 65%, according to a cumulative analysis by CNN polling director Jennifer Agiesta of all the Edison Research surveys conducted during the primaries.

Biden carried just 17% of Hispanics younger than 30 and 13% of whites; Sanders even beat him by about 2 to 1 among younger African Americans, otherwise Biden's strongest group . In this youngest age group, Agiesta's analysis found, Biden was weak not only among all races but also with both men and women. Though one of the central rationales of Biden's candidacy has been that he is better positioned to win blue-collar white voters, he carried just 1 in 7 whites younger than 30 without college degrees, almost exactly the same as his meager performance among college-educated whites in that age range.

It's difficult to precisely compare Biden's performance with young people in the multi-candidate 2020 race to Clinton's during her one-on-one 2016 contest with Sanders. But on one key measure, the former vice president performed even more poorly: Biden's nearly 50 percentage-point deficit to Sanders among voters younger than 30 was even greater than Clinton's 43-point disadvantage, according to Agiesta's analysis of all the exit polls conducted that year

Younger voters should be a core Democratic constituency this fall. Throughout his tenure, polls have consistently shown that Trump is deeply unpopular among the racially diverse, socially tolerant millennial generation, and Generation Z coming behind them, which will be voting in large numbers for the first time in 2020. In the latest national CNN poll, for instance, only about one-third of those 34 and younger said they approved of Trump's job performance.

These results are triggering an unpleasant sense of déjà vu for some Democratic strategists. In 2016, though Trump carried only about one-third of voters younger than 30, Clinton won only 55% of them, well below Obama's 66% in 2008 and 60% in 2012, according to exit polls. One in 11 of those younger voters backed third-party candidates in 2016, more than among any older age group.

Will young voters tune out November?

This time, Democratic strategists are confident that Trump is unlikely to improve much, if at all, with younger voters. And they are generally less worried about young voters peeling off to third-party candidates, since the Libertarian and Green parties are not offering alternatives as well-known as Gary Johnson and Jill Stein, their 2016 nominees.

"The fundamental reality is we are going to have less third-party voting because the third-party candidates this cycle are less compelling and in many key states they will fail to make the ballot," says McElwee.

Instead, most Democrats see lackluster youth turnout, especially among young people of color, as the principal risk to Biden. Younger voters did not vote in the numbers that even Sanders expected during the primaries. And many Democrats believe it's a real risk they could disappoint again in the general election, particularly given the added disruption of the coronavirus outbreak.

"These voters, generally, are disappointed in how the primary played out and aren't stoked to have to vote for an old white guy," says Democratic pollster Andrew Baumann, who has extensively surveyed younger voters. "And they were already disillusioned about politics because they understand that they're the first generation to be worse off than their parents' generation was, and now they're getting hammered economically by Covid -- there's a real danger that could turn them off from politics even further. And then you add potentially higher barriers to voting due to the virus, and there are a lot of headwinds that the Biden camp need to take seriously."

The Biden campaign expects that young people's widespread dissatisfaction with Trump will prompt them to turn out more than in 2016. But Democratic activists working to mobilize younger voters say that's unrealistically optimistic.

"If that were enough, it would make my life a lot easier," says Ben Wessel, executive director of NextGen America, a liberal organizing group. "But the choice is not Democrat vs. Republican, it's voting vs. not voting." Expecting Trump to motivate youth turnout on his own, he added, "is just not the facts on the ground."

NextGen was among a group of eight liberal youth-oriented groups that recently wrote Biden urging him to inspire younger voters by adopting a long list of "bold" ideas. The request included many proposals championed by two of the candidates Biden beat, Sanders and Warren, including reaching a carbon-free economy by 2030, canceling all student debt, severely restructuring immigration enforcement and imposing a wealth tax on large fortunes.

"Messaging around a 'return to normalcy' does not and has not earned the support and trust of voters from our generation," the groups wrote.

Tulchin, the pollster for Sanders, says Biden cannot ignore such warnings. "There's a huge opportunity for him to reset, but what I want his campaign to understand is that the consequences of not going big and bold is you could easily replay 2016," with disappointing performance among younger voters, he says.

But this is where the tightrope for Biden could get wobbly. Some Democratic strategists worry that adopting too many Sanders-style "bold" proposals in an effort to excite younger voters will alienate older voters, who tend to be more moderate.

Finding issues that appeal

Biden's strength among older voters could be a pivotal asset against Trump. Older voters were the key to Biden's victory in the primaries: Agiesta's cumulative analysis of the exit polls found that he beat Sanders by 2 to 1 among Latino seniors, almost 4 to 1 among white seniors and by a crushing 13 to 1 among African Americans older than 65.

Maintaining that strength, Biden led Trump among seniors comfortably in recent general election polling by CNN, Quinnipiac and NBC/WSJ and more narrowly in the latest Monmouth University poll. Though Pew and Grinnell College in recent polls still showed Trump leading with seniors, the overall direction of the surveys suggests that Biden might significantly improve on the Democrats' recent performance among older voters. Each Democratic presidential nominee since John Kerry in 2004 has lost seniors, a preponderantly white age cohort, by at least 5 percentage points, according to exit polls; Al Gore in 2000 was the last Democrat to carry them.

Wessel says that history shows it would be a mistake for the Biden campaign to assume he can hold their support among older voters through Election Day. "Those older folks who are currently supporting Biden, those are more fertile fruit for the Trump campaign to try and pluck," he says. "Those are a lot of the sort of folks who may have abandoned Hillary in the couple weeks before the general in 2016. So to me, relying on them as your safest path to victory feels like déjà vu."

But Ruffini, the Republican consultant, says Trump faces a real risk that Biden could sustain his improved performance with older voters. Using thousands of polling interviews from the massive nonpartisan Nationscape survey project run by UCLA and the Voter Study Group, Ruffini recently calculated that while Sanders ran better against Trump among younger voters, Biden ran considerably better against the President with older ones

"Even when they had 25 candidates to choose from in the primary, older voters were choosing Biden," Ruffini said. "So there does seem to be something a little bit more durable in that support, a little more sticky, than may have been the case for Hillary Clinton in '16."

The big question remains whether Biden can improve among the young without dislodging the old. Part of the answer, party strategists say, is tactical: improving his lackluster digital communication effort and enlisting respected pop culture figures to validate him with skeptical younger voters. (That process began last week when rapper Cardi B. hosted Sanders to discuss his Biden endorsement on an Instagram Live interview and singer Miley Cyrus did the same with Warren .)

But most agree that Biden also needs to find issues beyond higher education that he can use to signal greater ambition to young people without unnerving the older voters who respond to his calls for a return to "normalcy." Almost all of the Democratic strategists I spoke with agreed that expanding his proposals on climate change , an issue he has already embraced, offers Biden the best chance to reach both groups.

McElwee says his group's polling of primary voters has found that climate was a top concern for former Sanders supporters who expressed the most openness to voting third party in November. McElwee agrees that to avoid undermining his support with older voters Biden must "really ... put some limits" on how far he tilts left overall. But on climate, he argues, Biden can "go whole hog" in promoting a transition to cleaner energy sources "because there is no massive public opinion backlash, particularly not in a climate like this where we are looking at 20% unemployment."

Balancing these competing generational interests won't be easy for Biden. But the payoff for threading the needle between young and old would be enormous.

"If Biden were able to get his margin with old people and even Clinton's margin with young people," McElwee says, "the race would be over."