WASHINGTON — President Trump has spent two years publicly attacking the Federal Reserve and undercutting its chair, Jerome H. Powell. That animosity is making it difficult for Washington to project a united front as it stares down the most significant economic threat since the Great Recession.

The Fed has moved at breakneck speed to try to alleviate economic harm from the coronavirus pandemic, which is closing businesses, knocking workers off payrolls and almost surely plunging the economy into a downturn. Within weeks, the central bank has slashed rates to near-zero and enacted many of the programs developed during the 2008 financial crisis.

Despite the swift action, investors remain rattled.

That pervasive sense of insecurity comes in part as Americans struggle to decipher what kind of coordinated economic response Washington is staging. During the 2008 financial meltdown, Ben S. Bernanke, the Fed chair at the time, seemed to be moving in lock step with the Treasury Secretary and the White House. But that sort of comity has not been emanating from Washington during the current crisis.

Instead, Mr. Trump increased his criticism, even threatening to demote Mr. Powell as the crisis coursed through financial markets.