Elizabeth Warren took aim last week at another pillar of Wall Street's empire: the rental housing market. In a portion of her updated version of her ambitious 2018 housing bill, Warren proposed a check on the unregulated takeover of rental housing by the country's biggest investment firms. Instead of allowing Wall Street-backed developers to flip any distressed and foreclosed mortgage into a single-family rental unit, her bill would require the government to help keep the majority of these homes in the possession of individuals, community groups, and affordable-housing developers by setting aside a supply of mortgages that Wall Street can't touch.