Consumer spending has been the powerful and dependable engine of the current economic expansion. Americans have continued to shop through boom-time borrowing, high oil prices, on-and-off job growth, uncontrolled medical costs, rampant trade deficits, hurricanes and war.

Until last month, that is.

Major American retailers reported April sales declines that were among the worst on record. The pain was widespread, including discounters, department stores and specialty shops. Wal-Mart, the nation’s largest retailer, had the steepest decline since it began reporting monthly figures 28 years ago. Government retail figures for April confirmed the slump, showing the first decline in seven months.

Clearly, consumers are squeezed as gas prices rise and wage growth slows, and as declining home prices make it harder to borrow against the house. It seems that conditions will worsen before they improve.