Public officials who try to calm nervous financial markets with soothing words rarely succeed, as Steve Mnuchin learned Monday. The Treasury Secretary tweeted Sunday that America’s six largest banks told him in telephone calls that they had “ample liquidity” for lending and operations, and stocks promptly fell nearly another 3% on Monday.

Trading on Christmas Eve was thin and markets closed early, but maybe bank liquidity isn’t what investors are worried about. Stocks have fallen four straight trading days since the Federal Reserve again raised its benchmark interest rate and signaled no change in the pace of its quantitative tightening. Since the Fed’s announcement at 2 p.m. Wednesday, the S&P 500 had fallen 8.2% and the Dow Jones average by 8.1% through Monday.

Equity prices fluctuate, and the U.S. economy continues to grow, if more slowly heading into 2019 than in 2018. The Fed is obligated to focus on the real economy rather than the stock market, which has had a good long run. But the market reaction to the Fed’s decision has been negative enough to warrant some soul-searching inside the Eccles Building.

As we argued during President Trump’s search for a new Fed Chairman, the traditional debate about monetary hawks and doves isn’t helpful in this post-crisis era. The Fed is engaged in the unprecedented experiment of simultaneously unwinding its balance sheet and “normalizing” interest rates. Various sages may think they know how this is going to turn out, but we don’t. The wise course in this period is to pay close attention to current market signals—not merely lagging indicators like GDP and the jobless rate—and proceed with caution.

Mr. Trump complicates matters, as ever, with his criticism of Fed Chairman Jerome Powell. Apparently he has nominator’s remorse. But then anyone in Mr. Powell’s seat would have the same difficult task navigating the exit from nearly a decade of zero interest rates and record bond-buying.