The surprising resilience of the U.S. economy this year is masking underlying weakness among low- and middle-income households, as higher-income Americans continue to drive growth.

This dichotomy between the haves and have-nots isn¡¯t new, but the economic strain is now bleeding from the lowest earners to the middle class, creating an even starker divide that some economists say makes the economy more susceptible to a downturn.

The richest 10% of households are fueling nearly half of total U.S. spending, thanks to a stock market surge that has boosted wealth and in turn propelled economic output this year. Meanwhile, lower-income families are pulling back in the face of tight budgets, still-high living costs and a raft of corporate layoffs.