Trump’s campaign had a total of 5.9 million different versions of his ads, compared to Clinton’s 66,000, in a way that “better leveraged Facebook’s ability to optimize for outcomes,” the employee said. Most of Trump’s ads asked people to perform an action, like donating or signing up for a list, making it easier for a computer to measure success or failure. Those ads also helped him collect email addresses. Emails were crucial, because Facebook had a tool called Lookalike Audience. When Trump or any advertiser presented a set of emails, Facebook’s software could find more people who thought
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