There are several online petitions. One calls for the elimination of superdelegates altogether. Another asks superdelegates to align their choice with regular voters, not party elites, and it has more than 200,000 signatures.

But Sanders supporters point to the senator's string of recent wins and figure by the time the last vote is counted in California, he will have the popular lead. And then, under this scenario, it will be up to superdelegates, who make up roughly 15 percent of total convention delegates, to decide who gets the nomination.

Supporters cheer as Bernie Sanders speaks at a campaign event in Brooklyn, N.Y.

Mary Altaffer/AP

"Nobody is going to arrive in Philadelphia with enough delegates to win the nomination," said Jeff Weaver, Sanders' campaign manager. "And the superdelegates don't vote until you actually get into the convention process. So there's been a lot of talk about how the Republicans are going into an open convention. Well, the truth of the matter is, it looks like the Democrats are going into an open convention as well."

It's true that no one will likely have the 2,383 delegates needed for the nomination strictly out of the pledged delegates. But that's also because that number is a majority of all the voting delegates, which includes superdelegates.

The Sanders campaign still has its focus on winning as many pledged delegates as possible in the states still yet to vote, like New York, Pennsylvania and California and the campaign is trying to direct supporters looking to help to volunteering or organizing in those states. In fact the campaign's website lists hundreds of organizing events, many posted by volunteers, but the campaign has moved to remove any events related to reaching out to superdelegates.

Twitter Thayer, who answered questions over email, later changed the name simply to "Superdelegate List."

"The intent of the branding was to parody the famous Clinton Hit List, this was a tongue–in–cheek attempt at parody which I thought would encourage resharing," Thayer said. "The branding began to detract from the campaign's purpose, so it wasn't a hard decision to make the change once it was clear it wasn't working."

Thayer's goal with the site was to make it easier for voters to get in touch with superdelegates.

"The superdelegate system is rigged to protect establishment politicians and shut down populism," Thayer said. "Superdelegates, by their very nature, diminish the value of the vote by giving an elite constituency of representatives, party leaders, and even lobbyists extra power. The Superdelegate List exists to help voters challenge this undemocratic system. Contacting our elected representatives and party leaders and holding them to account is an American tradition. This is the only way to keep the voter base from being patronized or ignored."

"You should be ashamed of yourself," Ensley reads from a recent Facebook message she received. "Maybe you will do some soul searching and have some integrity and think about the decisions you're making and its implications."

"They said, you know, you should go to hell," said Ensley, describing another message. "How dare you vote against your own interests as an African-American woman. I expected you would be smarter than that."

"That is, that is very interesting," Elliott said after laughing uncomfortably. "As far as I know, this is probably only the second time I've been on a hit list, and the other one was not pleasant."

"Some of them will tell me, you know, how awful Hillary is, therefore, I should support Bernie, and then tell me how great Bernie is," said Elliott, who has known the Clintons since the 1970s. "And that's the kind of thing I think that is not helpful."

"Someone received my cellphone number, and they posted that, and so I'm getting calls on my personal cellphone from people all over the country," Martin said.

"It's likely that most callers are actually polite. If a few people contacting superdelegates are being obscene they'll of course drown out reasonable voices and harden opinions. However, it's useful to look at what's causing some of the anger and outrage we're seeing.

"Voters know they are being disenfranchised by superdelegate influence and these privileged voters are a reasonable target for frustration. And, let's be honest, if superdelegates aren't prepared to deal with the public, they shouldn't be party officials."

But all this freelance lobbying may be unnecessary. It has been the tradition of superdelegates, even in contentious primaries, to ultimately vote at the convention for the candidate with the most popular votes and pledged delegates.

"That was always done with the understanding that the voters would determine the outcome of this process, and I think they'll do it this time," Devine said back in February when the superdelegate controversy was flaring up after the New Hampshire primary.