Today, millions of voters across six states will cast their ballots for the two viable Democratic candidates left: former Vice President Joseph R. Biden Jr. and Senator Bernie Sanders. What began as a contest with historic diversity of race, gender and sexual orientation has come down to two heterosexual white men over 70. Astead W. Herndon, who covered Senator Senator Elizabeth Warren for The New York Times, asks: How did we get here? With Austin Mitchell and Jessica Cheung, producers for “The Daily,” Mr. Herndon traveled to Massachusetts to find out. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Ms. Warren’s position as one of the top-polling candidates early in the race made her a target for attack. Some say the personal criticism she weathered, especially from Mr. Biden, was sexist.She began her campaign with an avalanche of progressive policy proposals, but dropped out after failing to attract a broader political coalition in a Democratic Party increasingly, if not singularly, focused on defeating President Trump.