The holdout of some of the Bernie Sanders delegates who refuse to support Hillary Clinton at the Democratic National Convention expresses a theme of our politics: the value and obligations of membership in a community, against the purity of the individual vision of the good.

Sanders himself has come around to muting his policy differences with Clinton as she seeks to fuse her party together against Donald Trump. In this, Trump’s sheer offensiveness plays a unifying role. But the task is made more difficult by the concept of membership – Sanders himself has only recently registered as a Democrat. The deep roots of attachment are not there.

Sanders may be a recently minted Democrat but as a 74 year old professional politician he recognizes that a cohesive Democratic effort is essential to defeat Trump. As a talented politician named Ronald Reagan is reported to have said, “The person who agrees with you 80 percent of the time is a friend and an ally - not a 20 percent traitor.” But some of the Sanders followers eschew membership in the 80 percent community, as today’s New York Times reports:

Earlier in the evening, several dozen Sanders delegates paraded off in a coordinated demonstration against Mrs. Clinton’s nomination. Some of them said beforehand that they were attending their first Democratic convention and felt no party loyalty or compulsion to fall in line behind Mrs. Clinton, whom they described as insufficiently progressive on new banking regulations, a $15 minimum wage, a ban on fracking and other issues.

“I’m just not there yet in terms of supporting Hillary, because her words are only her words, and I don’t fully trust that she’ll act on our agenda,” said Ingrid Olson, 38, a delegate from Iowa.

Delegates like Ms. Olson, convinced of their own vision and rectitude, cannot sacrifice their individual wisdom to membership. Had Ms. Olson been around politics longer, she might be more aware that politicians do indeed attempt to live up to their promises when in office. They are held to it by their constituencies – membership is a two way street. Those who “feel no party loyalty or compulsion to fall in line” are not members – they are detached from the very organization they seek to change, and have no investment when the organization, made up of many more people with many more interests than any individual delegate, meets only 80 percent of their demands. By spurning their membership they forfeit the right and possibility of bending that 80 percent to 85 percent or 90 percent in the future. But they maintain their individual identities.

This is one reason why the Democrats should not have tinkered with the superdelegate rule. The superdelegates are fully committed members – congressman, senators, governors, and a few others who have devoted their lives to the Democratic Party. They’ve lived with it through change, including changes that may not accord with their own individual preferences. Superdelegates were intended to serve as a ballast against the heavy winds of populist revolt spurred by short term passions. In practice the superdelegates have most often fallen in line with the popular vote. Nonetheless a party with solid institutional structures is a party less likely to lose itself to a cheap demagogue and party outsider like Donald Trump.

The party nomination process has never been meant to serve a plebiscitary function. When parties function well they bring in and attend to divergent factions and interests within the party – groups that understand that sometimes you only get eighty percent. No one gets one hundred percent and when your candidate loses it is usually not because he’s been cheated but because he got fewer votes than the winner. That is the case here.