Since the article is behind a paywall I have added a link to the CBO’s long-term budget outlook.
The Federal Budget
The deficit increases significantly in relation to gross domestic product (GDP) over the next 30 years, reaching 8.5 percent of GDP in 2054. That growth results from rising interest costs and large and sustained primary deficits, which exclude net outlays for interest. Primary deficits are especially large given the forecast of low unemployment rates; those deficits average 0.6 percentage points of GDP more over the next 30 years than they did over the past 50 years.
Debt held by the public, boosted by the large deficits, reaches its highest level ever in 2029 (measured as a percentage of GDP) and then continues to grow, reaching 166 percent of GDP in 2054 and remaining on track to increase thereafter. That mounting debt would slow economic growth, push up interest payments to foreign holders of U.S. debt, and pose significant risks to the fiscal and economic outlook; it could also cause lawmakers to feel more constrained in their policy choices. [end quote]
Will the international bond market absorb such huge deficits without driving long-term interest rates up?
Will the Federal Reserve step in with QE, buying the debt to suppress interest rates?
Wendy
Does that really work though? If the Fed buys $5T of debt, aren’t they simply adding $5T of new money into the wild? And doesn’t that cause inflation to rise? And doesn’t that cause interest rates to rise (not fall)?
Looks like so far, us foreigners, in our eagerness to export our stuff to you, have been reliable suckers to buy your debt from the proceeds…
… (surely, it will all be paid back one day 
) so the Fed has actually been shrinking (gasp) its balance sheet for almost three years:
So, what will trigger the cycle to stop?
Only if money gets into the hands of the “wrong” people - see Covid-related handouts.
Right. iirc, the process is called “sanitizing”. Treasury sells bonds to banks. The Fed buys the bonds from the banks, with newly printed money. The banks then deposit the money with the Fed. The Fed pays the banks interest on the “excess deposits”.
Steve
To be fair, you don’t have much choice. Most international trade is conducted in dollars. After say, China sells a bazillion dollars worth of stuff to us, they now have a bazillion dollars sitting in the bank. What do you do with a bazillion dollars cash? Not much choice other than to buy US bonds.
When the Fed adds new money, they add it to the banks = QE. The banks decide whether to lend the money to consumers or invest it in assets. The banks have chosen to NOT lend most of the money to consumers but to invest in assets such as bonds (which suppresses interest rates), stocks and real estate. This has caused massive inflation in asset prices but not consumer price inflation.
When Congress adds new money it goes into the hands of consumers (lower taxes to individuals, giveaways such as the Covid bonuses). This increases consumer demand which causes consumer price inflation.
Wendy
Well, we used to be able to convert them into gold. Conceptually. When de Gaulle asked for it in earnest, we all know what happened -
Then again, we could choose not to build and send stuff for nothing more than debt…
Hmmm, I think this needs to be explained better. When the Fed acquires assorted bonds (and MBS) for $1T, are you saying that they hand newly created $1T to the banks in return for $1T of bonds/etc those banks hold? But then you are saying that the banks take that $1T and simply reinvest it into new bonds (and stock, etc)! So who exactly does the bank give that $1B to in return for those bonds (and stock, etc)?
If they give much of that new money to the government, then the government spends it (usually as quickly as possible) and hands it to various other people, businesses, employees, etc. And all those people now have more money (overall in the macro sense) to spend on goods and services … and that causes inflation.
And when they (the banks in question) buy an asset, they are handing over that cash to the owner of that asset, and then the former owner of that asset has cash to spend. Some of it gets reinvested of course, and that causes asset inflation. But some of it spent. Two ways. One, some may be spent by the owners who received the money. And two, when the money gets reinvested, the company it is reinvested into now has more money to spend on expansion, hiring, capex, etc. And that additional spending on “stuff” also fuels inflation.
This is why in the macro sense, adding an extra $1T of money into the economy usually will increase inflation. New money is new money, one way or another.