[2006alum]

As a first approximation, as long as:
structural deficit/GDP + interest * debt/GDP < GDP growth

You are fine indefinitely (debt as a percent of GDP goes down over time).  Interest rates have been at historic lows, so the second part of the equation is not a problem.  The issue is the structural deficit and lack of GDP growth.

BC

One thing that I have found useful to note with these kinds of models is that our intuitive understandings of economic production tend not to incorporate seemingly unrelated externalities like the costs of economic growth to the planet (and concomitant exacerbation of storms, droughts, etc.) as well as the increased likelihood in global pandemics that result from so much interconnectedness. The heightened costs of mitigating those externalities not only reduce growth (in terms of crop losses, folks out of work, etc.), but they also result in increased expenditures to offset it. 

These kinds of acts of god tend to be thought of as force majeure exigencies unrelated to the fundamentals of economic growth calculations, but of course both could be fairly incorporated as "negative externalities" associated with various growth strategies. For example, as this useful chart shows, our spending on cleanup related to weather and climate disasters has exploded over the past decade. And whereas prior pandemics took many months or years to make their way across the globe, our experience with COVID-19 shows how hard it is to contain a virus in an age of widespread interconnectedness.

Changing times can also make strange bedfellows - on this, I suspect many America Firsters and lefty environmentalists agree with some of the changes needed, even if their underlying motivations may be entirely unrelated to one another.

[2006alum]

As a first approximation, as long as:
structural deficit/GDP + interest * debt/GDP < GDP growth

You are fine indefinitely (debt as a percent of GDP goes down over time).  Interest rates have been at historic lows, so the second part of the equation is not a problem.  The issue is the structural deficit and lack of GDP growth.

BC

One thing that I have found useful to note with these kinds of models is that our intuitive understandings of economic production tend not to incorporate seemingly unrelated externalities like the costs of economic growth to the planet (and concomitant exacerbation of storms, droughts, etc.) as well as the increased likelihood in global pandemics that result from so much interconnectedness. The heightened costs of mitigating those externalities not only reduce growth (in terms of crop losses, folks out of work, etc.), but they also result in increased expenditures to offset it. 

These kinds of acts of god tend to be thought of as force majeure exigencies unrelated to the fundamentals of economic growth calculations, but of course both could be fairly incorporated as "negative externalities" associated with various growth strategies. For example, as this useful chart shows, our spending on cleanup related to weather and climate disasters has exploded over the past decade. And whereas prior pandemics took many months or years to make their way across the globe, our experience with COVID-19 shows how hard it is to contain a virus in an age of widespread interconnectedness.

Changing times can also make strange bedfellows - on this, I suspect many America Firsters and lefty environmentalists agree with some of the changes needed, even if their underlying motivations may be entirely unrelated to one another.