“Fitch’s decision is puzzling in light of the economic strength we see in the United States,” Yellen said in remarks prepared for an event in McLean, Virginia.

In the longer term, the US “remains the world’s largest, most dynamic, and most innovative economy – with the strongest financial system in the world.”

Yellen’s criticism is an echo of predecessor Timothy Geithner’s almost exactly 12 years ago, when he blasted S&P Global Ratings for “really terrible judgment” in becoming the first of the three most-cited ratings firms to remove the US from the top, AAA tier. Moody’s Investors Service is now alone in keeping the US at the highest grade.

Fitch late Tuesday cut the US to AA+, citing an erosion in financial governance, rising budget deficits and expected fiscal deterioration over the next three years.

Treasuries showed little immediate reaction to the Fitch move, but then slid Wednesday morning in the wake of stronger-than-expected jobs data. They accelerated their selloff following a bigger-than-expected plan for increased US debt issuance. 

Fitch analysts drew attention to medium-term fiscal challenges that they said have been “unaddressed.” By contrast, Yellen has expressed optimism about the longer-term debt picture, saying that inflation-adjusted interest costs aren’t historically high.

The Fitch statement also said the firm anticipates the US to fall into a mild recession in late 2023, a projection that’s at odds with the assessment of a number of economists. Wednesday morning, Bank of America Corp. scrapped its own forecast for a recession, becoming the first large Wall Street bank to officially reverse its call.

Yellen said the Fitch decision “does not change what all of us already know: that Treasury securities remain the world’s preeminent safe and liquid asset, and that the American economy is fundamentally strong.”

Earlier Wednesday, one of Yellen’s top lieutenants downplayed any risk of forced selling by investors now that Fitch rates the US at AA+.

“We did not see any evidence of that in 2011” with the S&P event, Treasury Assistant Secretary for Financial Markets Josh Frost told reporters Wednesday. “We continue to see robust demand for Treasury securities.”