DES MOINES, Iowa -- The day after Joe Biden announced he would not run for president in 2016, some supporters in Iowa did a surprising thing: They volunteered for their second-choice candidate -- Bernie Sanders.
It was an early indication of a counterintuitive dynamic at work four years later, now that the two men are running against each other. They are locked in an ideological struggle for Democrats' 2020 nomination that pits the politically moderate Biden, a classic party insider, against the liberal Sanders, a blow-up-the-system outsider. And yet they appeal to some of the same voters.
Both campaigns believe there is a swath of voters -- mostly white, working-class voters, including those who voted for Donald Trump in 2016 after backing Barack Obama twice -- who are torn between Biden and Sanders, the race's old-timers. Both men's campaigns are fishing in that electoral pond as each candidate looks to expand his base in a tight contest.
"There are a lot of working class voters who are up for grabs, and it is increasingly Joe Biden and Bernie Sanders who they are deciding between," said Ro Khanna, a co-chair of the Sanders campaign. "The more working class, the better Bernie does. And that is where we run into contention with Biden."
For all the punditry about candidates competing to dominate in ideological lanes -- and the recent attention on the personal feud between the left's marquee candidates, Sanders and Massachusetts Sen. Elizabeth Warren -- the competition between Sanders and Biden reflects how voters' decision-making is often far more nuanced, and divorced from standard political labels.
"They're both scrappy," said Sean Bagniewski, chairman of the Democratic Party in Polk County, Iowa, which includes Des Moines. "Ideology isn't as important as the personality. To a lot of folks, they feel like they know and can trust both Joe Biden and Bernie Sanders, regardless of the ideological stuff."
The latest Morning Consult/Politico poll of likely Democratic primary voters nationwide found that among Biden supporters, 29% said that Sanders was their second choice, more than any other Democrat in the race. Other polls show the two candidates in competition for the lead among non-college-educated white and Latino voters.
With the rivalry among top Democrats so intense, the Sanders campaign sees a clearer path to poaching voters from the Biden coalition than to exploiting what would seem the more obvious target of voters supporting Warren, Sanders' ideological soulmate.
"The Sanders folks realize the progressives with Warren are with her and there is no point in trying to out-progressive her," said Patrick Murray, director of the Monmouth University Polling Institute. "They need to find voters making a decision on a dimension other than ideology."
The Biden campaign is taking nothing for granted. It believes his edge over Sanders, as well as other rivals, is the perception that the former vice president is the most likely to beat Trump.