More than seven years after President Donald Trump launched his political career by questioning then-President Barack Obama’s citizenship, Democrats are still struggling to find the right strategy to fight back against his racially-charged rhetoric. After years of taunting from Trump, Sen. Elizabeth Warren revealed her DNA results this week proving her Native American roots. If it was an effort to take on Trump directly, it didn’t seem to work. The president continued his mocking references to her as “Pocahontas” and she managed to offend Native Americans who felt their heritage was being used as a political prop. […] As Democrats...