Mike Brest at the Washington Examiner reads the tea leaves:
"Maddow was one of the leading voices in the speculation surrounding the special counsel's report into whether or not the president or his campaign conspired with Russia to win the presidential election. In the week after Attorney General William Barr's letter to Congress where it was revealed that Mueller found no evidence of a conspiracy, Maddow lost half-a-million viewers, according to the Daily Beast.H/t: Geller Report
Her ratings continued to drop through the spring and into the summer. In June and July, her nightly average audience dipped below the 2.5 million marker only reaching 2,450,000 in June, but hit a little bump to 2,487,000 in July. The slight bump in July might be attributed to the recent revival of the report as Mueller himself testified before Congress."