Senator Elizabeth Warren has released a DNA test that provides “strong evidence’’ she had a Native American in her family tree dating back 6 to 10 generations, an unprecedented move by one of the top possible contenders for the 2020 Democratic nomination for president. Warren, whose claims to Native American blood have been mocked by President Trump and other Republicans, provided the test results to the Globe on Sunday in an effort to defuse questions about her ancestry that have persisted for years. She planned an elaborate rollout Monday of the results as she aimed for widespread attention. The analysis...