tl;dr Trump's team tested roughly 90X the variations of ads that Clinton's team did (5.9MM vs 66K), and aggressively utilized Facebook's powerful lookalike audi

tl;dr Trump's team tested roughly 90X the variations of ads that Clinton's team did (5.9MM vs 66K), and aggressively utilized Facebook's powerful lookalike audience tool, while Clinton used it for only 4% of her ads. Trump ads also allowed Facebook's ad algorithm to optimize for actions, where Clinton focused on simple exposure. In other words, Trump's team let the Facebook ads system do its thing, utilizing the same tools that other marketers on the platform use regularly. Hillary's team used it more like a traditional media buy, leaving Facebook's most powerful advertising features largely unused. To the extent that one believes Facebook ads had any effect on the election, this seems to at least partially answer the question of how things ended up where they did.