Here is my latest projection showing that public debt will exceed 150% of GDP in 2041. Compare to the previous forecast showing this would happen in 2049.
What is going to happen in 2041? Probably nothing. We don't know exactly what the limits are. But at some point it is clear that the system will totally break down. For example, look at the interest projection in 2041, which I have as $1,800 (million), which is about 3.8% of GDP. The latest Long-Term Budget Outlook by the CBO predicts that the average amount of interest, as a percent of GDP, after 2041 will be 7.0%. So for instance in 2043, if GDP is $50.1 trillion, then the interest paid in that year could be $3.5 trillion instead of the $2.0 trillion I have forecast in that year. The CBO projects that the Debt Held By The Public in 2051 will be 202% of GDP, which is much higher than my forecast. So my forecast above is conservative compared to what the CBO projects.
To go out a limb and do a little speculation, I think the dollar will be rejected internationally as a reserve currency after 2040, to be replaced by a cryptocurrency which does not currently exist. And I think the American Empire will collapse, similar to how the Soviet Union collapsed, and by replaced by several countries.
And this all may happen even sooner than my projection. The above chart assumes long-term inflation of 3.5%, but we have good evidence that 8% is a better number to use.
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Update: This is what the CBO says is likely to occur after 2040:
Persistently rising debt as a percentage of GDP would also pose significant risks to the fiscal and economic outlook, although financial markets currently do not reflect those concerns. In particular, that debt path would have these economic and financial effects: 1) It would increase the risk of a fiscal crisis—that is, a situation in which investors lose confidence in the U.S. government’s ability to service and repay its debt, causing interest rates to increase abruptly, inflation to spiral upward, or other disruptions—and 2) It would increase the likelihood of less abrupt, but still significant, adverse effects, such as expectations of higher rates of inflation, an erosion of confidence in the U.S. dollar as an international reserve currency, and more difficulty in financing public and private activity in international markets. https://www.cbo.gov/publication/57038