WASHINGTON — William Barr, President Donald Trump’s choice for attorney general, sent an unsolicited memo earlier this year to the Justice Department that excoriated special counsel Robert Mueller’s inquiry into potential obstruction of justice by Trump, saying it is based on a “fatally misconceived” theory that would cause lasting damage to the presidency and the executive branch.

The 20-page document, which was reviewed by The Wall Street Journal, provides the first in-depth look at Barr’s views on the special counsel’s Russia investigation, which he would likely oversee if confirmed.