It is the recognition that the US economy is immune to slowing global economic activity — which was already slowing before the COVID-19 pandemic.
The mystique surrounding US economic growth expectations, and particularly the potential for domestic inflation, has vanished. We may not be heading to Germany's -0.65% negative 10 year bond interest rate , but the bond market has come to see US government debt as the last remaining "bargain" in risk-free securities for what it is and is piling in.Typically, a collapse in bond yields of the present magnitude would set off flashing red lights signaling recession – if not worse.
In short: Take the free money being offered up by domestic and global holders of capital alike and put it to good use. Part of "getting to free" rests in the issue of how long a nation has to get to a positive marginal return on capital it borrows and invests. It is hard to reap the benefits of a new toll road before you have to pay back the bond in 10 years and the road takes all 10 years to build.