Mr. Trump has moved to add a new round of tariffs on Chinese products and to declare China a currency manipulator, while Beijing has canceled what officials had said would be new purchases of American agricultural goods. Economists warn that the moves will hurt growth in both countries, and that the Fed, in particular, has only so much help to give.

“Until the most recent escalation, it seemed that the Fed had at least been able to partly offset the drag from the trade war,” said Michelle Meyer, chief United States economist at Bank of America Merrill Lynch . “The Fed is attempting to sustain this recovery, and attempting to support growth, but there are clearly limits.”

After raising rates four times in 2018, Fed officials reduced them last week, to a range of 2 to 2.25 percent . Markets expect at least one more rate cut, and possibly two, before the year is out. That rate environment is abnormally low for an economy as strong as America’s has been during Mr. Trump’s term, the analysis by The Times shows.

The analysis draws on data from the Brookings Institution’s Hutchins Center on Fiscal and Monetary Policy and a monetary-policy gauge devised by a Stanford University economist. It found that since the final quarter of 2017, when the $1.5 trillion tax overhaul was enacted and unemployment was just above 4 percent , Mr. Trump has enjoyed unusually large levels of fiscal expansion and monetary accommodation for a period of such little joblessness.