The Federal Reserve embarked on a broad new effort Thursday to spur the economy just weeks before the presidential election, announcing an open-ended bond-buying program aimed at boosting the labor market until it improves “substantially.”

Eyeing an economic recovery that is treading water, and an unemployment rate that refuses to go down, the nation’s central bank said it was committed to buying $40 billion in mortgage debt every month. The Fed said the purchases would continue until the agency sees sufficient improvement in the nation’s labor market.