By Sue Halpern October 24, 2019 At a House Financial Services Committee hearing, on Wednesday, Facebook’s C.E.O., Mark Zuckerberg, struggled to elucidate his company’s political-advertising policy.Photograph by Al Drago / Getty In the course of the 2016 Presidential election, Donald Trump and Hillary Clinton spent eighty-one million dollars on Facebook ads. With a little more than a year to go until the next election, candidates have already spent more than sixty-three million dollars...