Better late than never: Attorney General William Barr has tasked U.S. Attorney John Durham to investigate the origins of the Trump-Russia investigation. If the Justice Department had done this two years ago, the country would be in a much better place.

Mr. Barr has made clear that he intends to restore his department’s credibility. The Durham appointment is a perfect example of that effort. This is how Justice ought to operate, from the nature of the probe to the choice of prosecutor. It’s a striking contrast to the hash that...