“The thing that Facebook does really well, and the thing that I learned pretty extensively at Facebook, is how to measure things,” Mr. Barnes said. “As I considered what I wanted to do after Facebook as I went through sort of this political transformation, I wanted to know: What is the best way that I could contribute to help defeat Trump in 2020?”

During the 2016 election, Mr. Barnes often used a Facebook tool known as “brand lift” to test different persuasion messages online for the Trump campaign. The tool provided insight into whether some of the online ads were moving people.

That tool has since been taken away from political campaigns by Facebook, part of its broad restructuring of how campaigns are allowed to operate on the platform following widespread backlash after the 2016 election.

Through his small team of engineers and data scientists, as well as ample cash from Acronym, which does not disclose its donors, Mr. Barnes has been able to recreate, to an extent, a similar tool.

“What’s felt impossible in the past is to test the real-world effect of ads of people who actually saw them, on an ongoing, consistent basis,” said Solomon Messing, the chief data scientist at Acronym. “And what we did was to develop a way to do this on Facebook.”

The tests are run in five states — Arizona, Michigan, Wisconsin, Pennsylvania and North Carolina (a full test involves selecting the audience, delivering an initial survey, running ads to half of the respondents, running the second survey to everyone and analyzing the results).

Using a voter file maintained by Acronym, the group casts a wide net for a list of names, based in part on voting history, propensity to vote for President Trump in 2020 and party registration. The group then sends those results in a list to Facebook to build an audience to advertise to in those five states.