(CNN)Democrats are days away from choosing a new party leader in a race that will help determine how to fight President Donald Trump. But to get there, they also are revisiting the bitter split of the 2016 presidential primary.Former Labor Secretary Tom Perez and Minnesota Rep. Keith Ellison are at the forefront of an eight-candidate field to chair the Democratic National Committee. Perez is picking up the endorsements of the heads of the Democratic National Committee's caucuses for women, Hispanics, Asian-Americans and rural Americans. Ellison is picking up the mantle of the insurgency that led to Sen. Bernie Sanders' presidential...