One of the Democratic Party’s top pollsters gave a presentation to senior members of former Vice President Joe Biden’s presidential campaign earlier this month making the case that Sen. Elizabeth Warren (D-Mass.) would provide the most upside as Biden’s running mate.

Stanley Greenberg, who advised the presidential campaigns of both former President Clinton and former Vice President Al Gore, presented a 14-deck slide to the Biden campaign detailing how the likely Democratic nominee needs to grow his support among young people and Democrats who did not support him during the primary.

The presentation warned that the biggest threat the Democrats face in 2020 is the “lack of support and disengagement of millennials and the fragmentation of non-Biden primary voters.”

Greenberg concluded that the intensity of support around Warren’s messages on corruption in Washington and an economy that is rigged against the middle class would help Biden win over remaining persuadable voters, while also rallying the left flank of the party behind his nomination.

"Senator Warren is the obvious solution,” Greenberg concluded in the presentation, which was obtained by The Hill. The presentation was first reported by Politico. 

The data Greenberg presented found Biden leading President Trump 47 percent to 42 percent in interviews with registered voters across 16 battleground states, a slight decrease from April, when Greenberg found Biden with a 48 to 41 lead.

The poll found Biden leading by 8 points on the question of who is best equipped to manage the pandemic. But 53 percent of voters in the poll said they trust Trump on the question of who would do a better job at getting people back to work — a potentially crucial metric as the economy begins to open up.

Greenberg argued that a lack of support from young people and from Democrats who did not cast ballots for Biden in the primary is a major outstanding issue for the campaign.

Ninety-four percent of those who voted for Biden in the primary say they’ll vote for him in the general election.

But only 79 percent of people who supported Sen. Bernie Sanders’s (I-Vt.) presidential campaign said they’d vote for Biden, compared to 11 percent who said they’d vote for Trump.

And only 73 percent of those who voted for someone besides Biden and Sanders in the primary said they will support Biden in the general election, compared to 17 percent who said Trump.

Greenberg also found that voter apathy toward Biden’s core messages of restoring the middle class and rebuilding America’s standing in the world was dampening enthusiasm for him among young millennials.

The poll found Biden leading Trump by 17 points among millennials, with 10 percent of millennials saying they’d vote third party. Some members of former Secretary of State Hillary Clinton’s presidential campaign blamed soft support from millennials on her 2016 loss. Exit polls found Clinton winning millennials by 17 points.

Greenberg made the case that the best way for Biden to win over non-Biden primary voters and young people is to add Warren to the ticket.

Warren’s message also resonates with Hispanics and white unmarried women, whom Greenberg identified as demographic groups where Biden still has potential upside support.

The veteran pollster tested Warren’s core messages of anti-corruption and anti-rigged economy and found those messages polled “off the charts” among the voters that Biden needs to reach.

“The Biden messages are competitive with Trump messages, but do not win intense support, and they are weaker than the Warren messages on corruption and rigged politics and the messages on working families,” Greenberg wrote.

“Warren’s corruption and rigged politics messages poll off the chart with non-Biden voters and millennials. Warren’s reform messages are also dominant with Biden’s ‘winnable voters,’ white working class women, and independents.”

The Biden campaign is in the midst of an intense vetting process as it seeks to pair the presumptive nominee with a female running mate.

In addition to Warren, the Biden campaign is reportedly vetting Sens. Amy Klobuchar (D-Minn.) and Kamala Harris (D-Calif.), as well as former Georgia state House Rep. Stacey Abrams (D), New Mexico Gov. Michelle Lujan Grisham (D), Rep. Val Demings (D-Fla.) and others.

Biden said at a fundraiser on Wednesday night that he hopes to have made a final decision by Aug. 1, about two weeks before the Democratic nominating convention in August.

Biden said he’s looking for someone he’s comfortable with, rather than an ideological ally.