In a primary, the information gathered by the campaigns becomes more important than a lot of the information in the voter file — and that’s why a breach by another campaign could be so important. The factors that usually predict whether individuals will vote for a Democrat or a Republican — like whether they’re registered in a party, whether they live in a heavily Democratic precinct or whether they’ve voted in a past Democratic primary — are far less powerful. It’s the data gathered by the campaigns, not the often-hyped consumer information (like what magazines a person might buy), that does the most work in campaign models.

In this context, the proprietary data held by the campaigns is a big potential advantage. The Clinton campaign, for instance, knows a lot about her supporters from the 2008 and 2016 cycles — the people who contributed to her, who volunteered, who attended her events, who signed up for her emails in two races. This information is far more useful than any statistical model, and it helps her campaign build stronger models, for good measure.

The Clinton campaign has also invested millions in survey research; it does not seem the Sanders campaign has done so. Survey data is the fuel for strong modeled estimates: Without it, you’re less likely to know the voter characteristics that tend to predict who will support a given candidate.

If the Sanders campaign was able to save the information necessary to know whom the Clinton team considered its strongest supporters, it would have been quite helpful: His campaign could then stay away from the voters who have supported Mrs. Clinton, and it would give the campaign an even better idea of its supporters.

This is what Sanders campaign officials attempted to do, and, according to Bloomberg News, they succeeded. Bloomberg reported that Sanders officials searched for and saved lists of voters who were modeled by the Clinton campaign to be among its likeliest supporters. For instance, they searched and saved a list titled “HFA Support 50-100,” which would include anyone deemed by the Clinton campaign to have a greater than 50 percent chance of supporting Mrs. Clinton. These support scores are informed by the powerful and proprietary data — on Clinton volunteers, past supporters, the Clinton campaign’s polling — that the Sanders campaign would not have otherwise been able to gain access to.

But it is not clear whether the Sanders campaign was able to retain this information. In a statement, NGP VAN said that unauthorized users were not able to export, save or act on unauthorized information. Instead, the Sanders campaign saved a one-page summary, according to the company. As I interpret it, the Sanders campaign was not able to save the valuable individual-level records that could have significantly improved its targeting efforts.

And for a few days, until a deal was reached, the Sanders campaign didn’t even have access to the basics.