Simply put, MMT is the idea that for a country that issues government debt in its own currency budget deficits don’t matter.   The government can simply print more money if it wants to spend more than it collects in taxes.

Although the theory has been around for a while (the first Google result I got was a critical opinion piece from almost a decade ago), it’s been revived recently by “progressive” Democrats arguing for dramatically increasing social welfare spending.  For them, the answer to the question “What about the Federal deficit?,”  is “MMT,” the government can always issue more debt/print more money.

MMT reminds me a bit of Modern Portfolio Theory (MPT), which was crafted in the 1970s and “proved” that the wild gyrations going on in world stock markets in the late 1960s and the first half of the 1970s were impossible.

Four issues come to mind:

–20th century economic history–the UK, Greece, Italy, Korea, Thailand, Malaysia, lots of Latin America…   demonstrates that really bad things happen once government debt gets to the level where investors begin to suspect they won’t be repaid in full.

This has already happened three times in the US: during the Carter administration, when Washington was forced to issue Treasury bonds denominated in foreign currency; during the government debt crisis of 1987, which caused a bond market collapse that triggered, in turn, the Black Monday stock market swoon a few months later; and during the Great Bond Massacre of 1993-94.

In other words, as with MPT, the briefest glance outside through an ivory tower window would show the theory doesn’t describe reality very well

–the traditional case for gold–and, lately, for cryptocurrencies–is to hedge against the government tendency to repay debt in inflation-debased currency.  In other words, every investor’s checklist includes guarding against print-more-money governments

–excessive spending today is conventionally (and correctly, in my view) seen as leaving today’s banquet check to be picked up by one’s children or grandchildren.  In the contemporary cautionary tale of Japan, the tab in question has included massive loss of national wealth, a sharp drop in living standards and economic stagnation for a third of a century.  No wonder Japanese Millennials have a hard time dealing with their elders.

Why would the US be different?  Why are Millennial legislators, of all people, advocating this strategy?

–conventional wisdom is that the first indication that a government is losing its creditworthiness is that foreigners stop buying.  This is arguably not a big deal, since foreigners come and go; locals typically make up the heart of the market.  During the US bond market crisis of 1987, however, the biggest domestic bond market participants staged the buyers strike.  Something very similar happened in 1993-94.  I don’t see any reason to believe that the culture of the “bond vigilante” has disappeared.  So, in my opinion, the negative reaction to a policy of constant deficit spending in the US is likely to be severe and to come very quickly.