Sexism is driving women away from the GOP front-runner Donald Trump and the Republican Party, potentially providing a windfall to Hillary Clinton in a general election. But to ride women's discontent into the Oval Office, of course, Clinton has to win the Democratic nomination. And while she has maintained a strong advantage with women voters overall, she's not doing well with all women. White millennial women favor Bernie Sanders. Perhaps that's because the best rationale for Clinton's candidacy hasn't been effectively communicated to millennial women. There is a powerful case to be made for electing a woman president, and it...