Sanders has not yet earned an outright majority in either of the two states he has won, and he is unlikely to in either South Carolina or any of the 14 states that cast ballots on Super Tuesday. The fact that he still leads the pack and appears in such a strong position to consolidate his edge illustrates the fundamental problem faced by Democrats who oppose Sanders.

In a way, it has to do with toothpaste.

For months, Democratic primary voters have at turns celebrated and bemoaned the largest primary field in their party's history.

There were simply too many options, too many candidates to love, to narrow it down to a final choice. Democratic voters and activists openly mourned when even candidates who failed to catch fire ended their campaigns. Their angst over having to finally settle on a nominee left some in political paralysis.

In the past, Iowans famously maintained their lists of three or four candidates for whom they could caucus. This cycle, Democrats across the country feel the same immutable indecision.

That anxiety borne of vacillation is what the psychologist Barry Schwartz identified in his 2004 book "The Paradox of Choice."

It is the feeling a shopper gets when faced with dozens of brands and types of toothpaste or deodorant or shampoo at the grocery store. A decision between dozens of options is far more difficult than a decision between just two. The breadth of choice can have a negative impact on happiness.

That same paradox is at play within the Democratic primary. The more attractive the options, the harder it has been for a voter to settle on a final answer.

The Democratic field has never fit into neat boxes. All along, primary voters have been searching for their most electable candidate, and unable to decide whether that person is a moderate who can appeal to the middle or a liberal who fires up the base.

"You want somebody who can take Trump down," said Greg Rosebeck, an internet executive here who walked into his caucuses torn between Biden and Warren.

"Nobody thought Trump was going to get elected. I know there's some fear about Bernie and the socialist, democratic socialist moniker, but you know, 2016 was a surprise for everybody, at least for me, and 2020 can be as well," said Don Seiersen, a freelance creative director who caucused for Sanders on Saturday. "Now seems like the opportunity for some change, and to jump on it. We may never get this opportunity again."

The contrast between Democrats who cannot decide on a non-Sanders consensus and the Sanders backers who show up en masse is the paradox of choice: One group has too many options. The other has only two, Sanders or not Sanders.

The indecision of the anybody-but-Sanders faction is exacerbating itself. In the past, campaigns collapsed when the money dried up. But Democrats this year have so incentivized and democratized small-dollar donors — going so far as to make them a criterion by which candidates qualified for the debate stage — that those donors are keeping alive several candidates who might otherwise have run out of cash.

Those small-dollar donors, many of whom contribute to multiple candidates, respond to viral moments and upset results; Buttigieg pulled in millions after winning the Iowa caucuses. Klobuchar raised millions more after a strong pre-New Hampshire debate. Warren's fiery performance at the pre-Nevada debate earned her more than $5 million in contributions.

The lesson they must learn is that winnowing the field is as much the responsibility of the candidates themselves as it is of the voters. If none of the candidates currently hunting for that next viral moment, that next breakthrough performance, that elusive first win pull the plug on their own ambitions, they will all be speaking at Sanders's convention coronation.

The toothpaste aisle remains cluttered, even if several of the brands aren't actually selling.