WASHINGTON — Stanford University law professor Pamela Karlan, best known for her 2019 testimony in favor of impeaching then-President Donald Trump, quietly left the Justice Department this month as a conservative group ratcheted up attacks on an “unethical” arrangement in which she continued to earn nearly $1 million a year from Stanford while working for the government. Karlan joined the department on Feb. 8, 2021, shortly after President Biden’s inauguration, and served about 17 months as principal deputy assistant attorney general for civil rights before she departed on July 1 with little fanfare. Karlan’s role was slated to last until...