After U.S. debt soared to $38 trillion, the ‘easy times’ are now over as hedge funds jump into the bond market, former Treasury official warns

The holders of U.S. debt have shifted drastically over the past decade, tilting more toward profit-driven private investors and away from foreign governments that are less sensitive to prices.

That threatens to turn the U.S. financial system more fragile in times of market stress, according to Geng Ngarmboonanant, a managing director at JPMorgan and former deputy chief of staff to Treasury Secretary Janet Yellen.

Foreign governments accounted for more than 40% of Treasury holdings in the early 2010s...