Concerns over America's fiscal outlook are mounting. Long-dated Treasury yields are at their highest levels since 2007, while the national debt has surpassed $40 trillion. It is not the first time Washington has faced an imposing financing challenge. Treasury Secretary Scott Bessent says the U.S. can grow out of the debt. But history suggests that when the Treasury cannot rely on the usual mix of investors, instruments and market conditions, it has also created new methods to raise funds.