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That prospect suggests one of the crucial questions in the Democratic primary will be whether Biden can sustain his big early advantage with older voters. Democrats skeptical of his candidacy generally believe that edge is ephemeral, based mostly on the fact that older voters are more familiar with his long career, especially his eight years as vice president for Barack Obama. Particularly among older African Americans, Biden’s support “is all very soft and it is all Obama,” says Bakari Sellers, a former South Carolina state representative who is supporting Senator Kamala Harris.

But Democrats sympathetic to Biden, and even many neutral observers, believe that Biden’s gray edge will endure. Only a little more than one-fifth of Democratic voters ages 45 and older described themselves as very liberal in 2016; about twice as many described themselves as moderate or conservative. Dick Harpootlian, a South Carolina state senator supporting Biden, told me that older voters are more measured about how far left the party can move and still defeat Donald Trump.

“Older Democrats have seen what happens when we shift to these positions that are untenable,” Harpootlian said. “I think older voters would tend to be more pragmatic, and by that I mean simply the assessment going on is, What’s the goal of this election? The vast majority of Democrats, I think, are pragmatic about that. Who is our best choice to go toe to toe with Donald Trump in 2020? Clearly, in my mind, it’s Joe Biden.”

Since Biden joined the race, age has quickly emerged as a significant chasm—dwarfing other, traditional Democratic divides in early polling. In CNN’s first national poll after Biden entered, the former vice president drew 45 percent of likely Democratic primary voters older than 45, four times as much as Sanders, his nearest rival. Among voters younger than 45, Biden also led, but only by 31 percent to 19 percent.

Despite the presence of six women candidates, an unprecedented number, surveys have not found a meaningful gender gap in support for Biden—or even a preference among female voters for the female candidates. Early polls have also failed to show much of a difference between college-educated and non-college-educated whites, though that cleavage—what I’ve called the “wine track” and the “beer track” in Democratic-primary politics—has shaped other contests. Even race hasn’t yet been a pivotal factor, with Biden leading among African American voters, despite the presence of two major black candidates: Senators Harris and Cory Booker.

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Firehouse Strategies, a Republican consulting firm, has joined with Optimus, a data-analytics company, to poll the three key early Democratic-primary states. The surveys they released in early May showed a stark age divide. In Iowa, they found that among Democrats ages 18 to 35, Biden drew just 17 percent, placing third behind Sanders and Senator Elizabeth Warren. But Biden opened a narrow lead over Sanders with voters ages 35 to 55, and then spiked to 41 percent among those 55 and older, four times the support of his nearest rival, South Bend, Indiana, Mayor Pete Buttigieg.