The sense of euphoric inevitability that prevailed when Republicans gathered in Milwaukee for the party’s nominating convention is gone. Victory, once all but assured, is now in doubt. The Trump campaign has struggled to break into the Kamala Harris–dominated news cycle in a positive way. And maybe most dispiritingly, the press now has something to prove — not to news consumers, who were let down by its effort to whitewash Joe Biden’s deteriorating condition, but to those who counted on...