Just before the release of the Mueller report, Attorney General William Barr reminded Congress that another report is coming soon. Justice Department Inspector General Michael Horowitz is wrapping up his related probe focusing on how the government handled the Trump-Russia investigation. If history is any guide, Mr. Horowitz will lay out the facts objectively, accurately, and in meticulous detail. His office produced a 514-page report on Operation Fast and Furious and a 568-page report on the Clinton email controversy. Both were widely accepted as authoritative due to the quality of the work and Mr. Horowitz’s credibility as neutral and fair. It’s a remarkable record in a country increasingly divided along partisan lines.