Matthew G. Whitaker, President Trump’s pick to temporarily helm the Justice Department, provides Trump with the leader he has long sought at the law enforcement agency: a political loyalist critical of the special counsel probe. Before Whitaker joined the Trump administration as a political appointee, the Republican lawyer and legal commentator complained that special counsel Robert S. Mueller III’s investigation of Russian interference in the election and of the Trump campaign was dangerously close to overreaching. He suggested ways it could be stopped or curtailed and urged his followers on Twitter to read a story that dubbed the investigators “Mueller’s...