U.S. debt has ballooned from ~$8 trillion to $40 trillion over the past two decades. At the same time, China and Japan—historically the largest foreign holders—have slashed their share of publicly held U.S. debt from 20.5% to 5.4%.

With traditional buyers backing away, the question becomes: who absorbs the flood of new Treasury issuance?

One analyst's bet: the Fed will step in and print.