President Ronald Reagan had been slowly chipping away at affirmative action since taking office in 1981, but it was six months into his second term that his administration saw its chance to deal it a decisive blow. Reagan and his Cabinet viewed his resounding electoral victory against Walter Mondale in 1984 as a mandate to end the Lyndon B. Johnson-era policy requiring all government contractors to take “affirmative action” to end discrimination at their firms. By the mid-’80s, that meant some of the country’s largest companies — such as General Motors, IBM and Merck — had implemented robust affirmative action...