Hillary Clinton and Bernie Sanders reached a detente at a debate Saturday night over a voter data feud that had ratcheted up in the hours before the event.

"Not only do I apologize to secretary Clinton, and I hope we can work together on an independent investigation from day one. I want to apologize to my supporters," Sanders said. "This is not the type of campaign that we run. And if I find anybody else involved in this, they will also be fired."

Clinton accepted the apology, adding: "I don't think the American people are all that interested in this."

The fight is over a real incident. Sanders staffers took advantage of a data breach to access some of Clinton’s proprietary voter information, according to an audit that became public Friday. The consensus from reviews of the audit is that the staffers did attempt to benefit from Clinton's information, but they didn't pull it off. They made lists of voters, but didn't take the step of downloading the data.

The Sanders campaign fired a staffer and has launched an internal investigation, Sanders said at the debate.

The Clinton campaign had seized on this incident. Saturday evening they posted questions on the campaign blog they want Sanders to answer personally, as reported by POLITICO. "Why did your campaign [initially] say it was an accident?" asked Jennifer Palmieri. "Why did the Sanders campaign claim that only one staffer was involved in accessing Clinton campaign data?"

The Democratic National Committee had suspended the Sanders campaign’s access to the data platform, called NGP VAN, which hosts all voter information for the Democrats. (VAN stands for "voter access network.")

Sanders had filed a lawsuit against the DNC on Friday afternoon. The campaign manager accused the committee of "actively

attempting to undermine our campaign." The campaign's access was restored on Saturday.

Related The 6 biggest policy differences between Bernie Sanders and Hillary Clinton

"They acquired the materials they needed to build the warhead, but

they never constructed it and armed it," said Ethan Roeder, the data

director for both of Barack Obama's presidential campaigns. Roeder reviewed the audit.



In that light, the accusations - coming from both the DNC and the

Clinton Camp that millions of dollars worth of data had been stolen - appears overblown.

Sanders has been in an ongoing struggle with the DNC since the beginning of the primary. The DNC has pretty openly lined up behind Hillary Clinton, pushing for her to cruise to victory without splitting the field, as happened in 2008. The Sanders campaign sees the punishment as driven by the DNC's broader bias against their candidate.

The database in question holds the key to the master Democratic voter file

NGP VAN is a data technology company that allows campaigns to view a whole host of information about voters across the country who have voted for Democrats in the past.

The DNC owns the basic voter file, which it shares with primary candidates running as Democrats. This includes all three presidential candidates as well as anyone running for lower offices on the national and state levels.

From there, each campaign can take those voters profiles and make all sorts of models with them, usually to predict how persuadable they are or how likely they are to vote, say on a scale from one to 100. Models can also be used to predict voters positions on specific issues, which helps campaigns target them.

During Obama’s 2012 campaign, for example, staffers used this type of modeling to figure out which undecided voters to target for canvassing and which voters seemed less motivated and could use an extra push.

The data and sources the system can pull in are incredibly precise because they rely on detailed information about every voter — rather than something like a poll, conducted with a small sample of respondents. For that reason, these models are very expensive to build.

Campaigns share the basic voter file, so they’re looking at all the same voters. But NGP VAN puts up firewalls between them so each campaign doesn’t have access to the other’s modeling.

What’s key to understand here is that the data hosted on NGP VAN's dictates a campaign’s entire ground game, which both of Obama’s campaigns claimed as their winning advantage. Losing access to the system means that a campaign loses its own predictive models dictating which voters to target – but it also means the campaign doesn’t have access to the names of Democratic voters.

Jeremy Bird, who directed the field operation for President Obama's 2012 campaign (a position that relied entirely on the power of this software), expressed outrage on Twitter.

They stole millions of dollars of research. This isn't a small thing. — Jeremy Bird (@jeremybird) December 18, 2015

Firing staffer isn't enough. They still have all files w targeting info. Explain how you are going to ensure these are & were never used — Jeremy Bird (@jeremybird) December 18, 2015

The value the system provides is not one that’s easily replicated, especially not this late in the primary.

What exactly did the Sanders campaign do?

For about 40 minutes on Wednesday, the Sanders campaign noticed that a glitch in NGP VAN’s system had caused the firewall between his campaign and that of Hillary Clinton’s to go down. So, theoretically, her campaign also had access to his proprietary data – though there aren’t any reports that her campaign tried to access them.

NGP VAN, which has the ability to closely track any information that user’s access or download, found in an audit that four Sanders staffers had accessed the Clinton data without authorization.

Bloomberg’s Jennifer Epstein obtained an audit of the breach which showed the staffers downloaded several lists of information on voters in 10 key early voting states, such as low support Hillary voters in Iowa and on-the-fence voters in New Hampshire.

Sanders staffers never actually downloaded the data they sought to find, according to Roeder, staffers typically save searches when they intend to come back to the data later on.



Even so, the information they looked at probably wouldn't have added

much value to their own data operation, since the searches were so

general.

The Sanders' campaign has admitted fault. "[S]ome of our staffers irresponsibly accessed some of the data from another campaign," wrote campaign manager Jeff Weaver in an email to supporters. "That behavior is unacceptable to the Sanders campaign and we fired the staffer immediately and made certain that any information obtained was not utilized. We are now speaking to other staffers who might have been involved and further disciplinary action."

The DNC announced that it would end Sanders’ suspension if it became clear the campaign had not used the information in any way. So far, it’s not clear whether any information has been used.

Why did the DNC react so severely?

The DNC has disciplined the Sanders campaign by essentially cutting it off from all the critical information it needs to canvass voters. The Sanders campaign has argued this is an overly stringent punishment, and indicated it’s part of the DNC’s larger prejudice against the Sanders campaign.

"The leadership of the Democratic National Committee is now actively attempting to undermine our campaign," wrote Weaver. "This is unacceptable. Individual leaders of the DNC can support Hillary Clinton in any way they want, but they are not going to sabotage our campaign - one of the strongest grassroots campaigns in modern history."

The DNC argues that the offense here was serious, and its actions are exactly what the Sanders campaign would demand if Clinton staffers had done this to them.

"The Sanders campaign doesn’t have anything other than bluster at the moment that they can put out there," DNC Chair Debbie Wasserman Schultz said on CNN. "It’s like if you found the front door of a house unlocked and someone decided to go into the house and take things that didn’t belong to them."

It's not much of a secret inside the Democratic Party that the DNC has favored Hillary Clinton's interests throughout the primary. Martin O'Malley, for instance, has criticized the organization harshly. "This is totally unprecedented in our party's history," he said, referring to the thin debate schedule, where most of the debates occur before the Iowa caucuses, and some were scheduled, unusually, for Saturdays. "This sort of rigged process has never been attempted before."

This is why the fight between the Sanders campaign and the DNC has gotten so brutal, so fast. To the DNC, the Sanders campaign committed a grave sin, and it isn't inclined to view the campaign's actions generously. To the Sanders campaign, the DNC is using this infraction as an opportunity to give Hillary Clinton one more advantage in the primary.