John Wagner

While the Clinton campaign’s reliance on analytics became well known, the particulars of Ada’s work were kept under tight wraps, according to aides. The algorithm operated on a separate computer server than the rest of the Clinton operation as a security precaution, and only a few senior aides were able to access it.

According to aides, a raft of polling numbers, public and private, were fed into the algorithm, as well as ground-level voter data meticulously collected by the campaign. Once early voting began, those numbers were factored in, too.

What Ada did, based on all that data, aides said, was run 400,000 simulations a day of what the race against Trump might look like. A report that was spit out would give campaign manager Robby Mook and others a detailed picture of which battleground states were most likely to tip the race in one direction or another — and guide decisions about where to spend time and deploy resources.

The use of analytics by campaigns was hardly unprecedented. But Clinton aides were convinced their work, which was far more sophisticated than anything employed by President Obama or GOP nominee Mitt Romney in 2012, gave them a big strategic advantage over Trump.

So where did Ada go wrong?

Somewhat related: Connected Math.