The rescue package being debated in Washington would involve at least $1.6 trillion of government spending, representing just a few weeks of lost economic activity. But the hit will almost certainly be vastly larger than that, analysts say, requiring multiple congressional interventions to come close to offsetting the fastest economic shutdown in American history.

The Federal Reserve stepped into the breach on Monday with strong action to prop up wobbly credit markets. And it promised efforts to aid small and midsize businesses that are failing in large numbers, a main street lending program that could multiply the power of the congressional spending package.

But that did not ease fears in the stock market, where the Dow Jones Industrial Average fell 3 percent to 18,591.93 — the lowest since November 2016. It remains unclear whether the Fed’s actions will be up and running fast enough to ensure that when government officials do flip the lights back on, a functional economy will be capable of a swift bounce back. Stocks rebounded strongly on Tuesday as hopes rose for agreement on the stimulus package.

“A $1.5 trillion stimulus package sounds like a lot, and it is,” LPL Financial Equity Strategist Jeff Buchbinder said in a note to clients. “But given the unemployment rate might be headed to double digits and many impacted businesses won’t survive through the spring without some help, it probably won’t be enough.”

Economists are now mostly just debating how deep and lasting the economic downturn will be. “The U.S. economy has entered recession as the COVID-19 outbreak and public health efforts to combat it have led to a sharp contraction in economic activity,” Gus Faucher, chief economist at the PNC Financial Group, wrote in a research note. “Restrictions on movement throughout the country have led consumers to pull back on their spending, with restaurants, hotels, movie theaters, entertainment venues, sports leagues, and many retail establishments closed. The airlines are rapidly cutting capacity, and U.S. auto manufacturers have stopped production.”