Americans are mad about inflation. McDonald’s just admitted they were right.

McDonald’s new $5 Meal Deal debuts Tuesday. For the next month, customers can get a McChicken or a McBurger, four chicken nuggets, a side of fries and a small drink for less than the price of a single Big Mac. The highly publicized, limited-time promotion seems to mark a change in the battle over inflation — and it’s a sign that, finally, people — and the government — are successfully fighting back against rising prices. 

Yes, the inflation rate in the U.S. is slowing. In May, prices were up 3.3% from a year earlier, down from...