Sanders and his supporters have called for the Democratic Party to allow for independent voters to vote in presidential primaries. Part of this is philosophical, because Sanders is an independent (although he caucuses with Democrats in the Senate). But part of this is political: Sanders has performed better in state primaries where independents are allowed to vote.

Instead, look at the way the California primary is being conducted. It's a big problem for Bernie Sanders.

Polls of next week's California Democratic primary are tightening , but they could be as unpredictable as the ones that were extremely wrong in Michigan several weeks ago. And this time it may not be the pollsters' fault.


In the case of California, Sanders got his wish. Tuesday's primary is open to "NPP voters," or those who registered with No Party Preference. Logistically, these voters will automatically receive an NPP ballot, and then they must request another ballot if they want to vote in the Democratic, Republican, or Libertarian primary.

This might be even more confusing for those NPP voters who request a mail-in ballot. They will need to request two different ballots from the outset. What's more, if voters return the NPP ballot without the presidential primary ballot attached to it, they won't be able to request the presidential ballot later. It will be marked down as if they have already voted.

Registered Democrats, among whom Hillary Clinton gets more support, don't have these hurdles. They simply vote on contested races on a single Democratic Party ballot.

This issue has concerned Sanders supporters in California for a while but has not received the same attention nationally. Recently, Sanders supporters sued the state, hoping to extend the deadline for voters to change parties, but they were rejected. The judge in the case said California voters were smart enough to understand the process.


All of this makes the California primary really difficult to poll. It is tough enough to identify who might vote in a low turnout primary, but it's even more difficult to figure which of the NPP voters will actually receive both ballots on Tuesday.

James Pindell can be reached at james.pindell@globe.com. Follow him on Twitter @jamespindell or subscribe to his daily e-mail update on the 2016 campaign at bostonglobe.com/groundgame.