James Fields Jr., the white supremacist who murdered a woman two summers ago when he steered a Dodge Challenger into a crowd of peaceful demonstrators in Charlottesville, Va., was sentenced Friday to life in federal prison. Lawyers for Mr. Fields, 22, had pleaded for mercy, citing his difficult childhood and mental health problems. Prosecutors had sought the life sentence, arguing that Mr. Fields’s racist, anti-Semitic beliefs motivated the decision to attend the white supremacist rally in Charlottesville and to attack counterprotesters, killing Heather Heyer and injuring dozens of others. “The defendant’s crimes were so horrendous — and the maiming of...