The Sanders campaign has filed a federal lawsuit against the state of California that seeks to extend the voter registration deadline all the way to primary day, June 7.

At issue are the confusing rules governing presidential primaries versus statewide elections.  The campaign wants a judge to order registrars in several counties to make a better effort to educate voters while giving Californians more time to register.

Los Angeles Times:

The lawsuit names the registrars of voters in San Francisco and Alameda counties as well as Secretary of State Alex Padilla as defendants.

A spokesman for Padilla on Sunday declined to comment on the pending litigation.

The suit focuses on whether "no party preference" voters who intend to cast ballots by mail understand they can ask for a ballot from one of the three parties that allow them to cross over and participate in the race for president: the Democratic Party, the Libertarian Party, and California's American Independent Party.

If they do not make the request, those voters will receive a ballot with a blank space where partisan ballots list the presidential candidates.

The lawsuit alleges that some counties have not done an adequate job of informing these voters. A recent report by Political Data Inc., a company that is paid to analyze California voter information for candidates and campaigns, found relatively few unaffiliated voters have asked for a ballot with presidential candidates.

As of last week, only 9% of "no party preference" voters in Los Angeles County had been mailed a Democratic ballot.

Neal Kelley, registrar of voters in Orange County and president of the state association of elections officials, said that about 23% of his county's "no party preference" voters have asked for partisan ballots. And he said that the outreach effort was carefully planned.

"Counties have been gearing up for this for well over a year," Kelley said.

While he would not comment on the allegations contained in the federal lawsuit, Kelley said it's not possible for elections officials to register voters on election day. California has plans to move to a "same-day registration" system in 2018 after certifying its new statewide voter database.

In the meantime, the current elections process relies on paper documents at each polling place listing eligible voters.

"The infrastructure's not in place," said Kelley.

California has been conducting "non-partisan" elections for a few years, where the top two candidates in the primary face off in the general election regardless of party.  But the Sanders campaign worries that independents aren't aware that they can vote in the Democratic primary, given that the contest is open to all.  The GOP primary is closed to anyone not a Republican.

No doubt, if successful, the extended registration period will benefit the Sanders campaign.  But Clinton has been pouring resources into the state, which is the most expensive media state in the country.  It's not clear if the bump Sanders will get can offset Clinton's enormous advantages in organization.