When the world's most recognizable fast-food chain stumbles, it rarely speaks only of burgers — it speaks of budgets. McDonald's second-quarter earnings, arriving before Tuesday's opening bell, arrive as a kind of referendum on the financial endurance of ordinary American households, already strained by fuel costs at four-year highs and a stock market that has quietly priced in $40 billion worth of doubt. The question Wall Street is really asking is not whether McDonald's will meet its numbers, but whether the people who depend on ninety-nine-cent meals are still holding on.