alt Hacker NewsJapan is the model of low interest rate debt and the US is not close to how low Japan was able to go, with a currency (Yen) vastly less potent than the global reserve currency.
Most of the US borrowing is domestic, very little of it is now foreign. No foreign entity can afford to absorb $2 trillion of new paper every year. That's equal to the total holdings of China + Japan. Going forward you might as well regard all US Govt borrowing as domestic, as that will essentially be the case given the scale. The UK holds $885b of treasuries, what are they going to buy annually that will make a difference at this point?
Every nation has a limitless ability to borrow internally via currency debasement, with obvious consequences. That USD debasement is why gold has gone up 10x in 20 years when priced in dollars. It's why healthcare and housing is so expensive - when priced in dollars. Cash pushed into gold in 2005, $100k, would now buy you a million dollar house. It's the dollar of course that has been hammered (among other currencies, the Euro has not done well against gold either).
The US won't stop being able to debase its currency and buy its own debt. What the US is doing is eating its hand. If it continues to get worse, it moves on to eating its arm, and so on (the US is de facto consuming its national wealth through stealth confiscation via currency destruction, rather than paying the bills with taxation directly).
>what are they going to buy annually that will make a difference at this point
Mechanically, "they" being sovereign banks serve as price-insensitive marginal buyers that close treasury auctions regardless of price because they buy treasury for storage/liquidity. VS domestic buyers (hedgefund insurance), who are price sensitive = raise rates to attract discriminate buyers who buy for yield/valuation = worse debt servicing = faster debasing. Foreign sovereign buyers still play governor role in making sure domestic buyers get a shit none-market deal, i.e. US gov gets a good deal which moderates velocity of debasing. Of course past certain level of debt brrrting, the ability for sovereign buyers to absorb is compromised, in which case it makes sense for US to fuck foreign buyers over and inflate away as much debt as possible while still reserve currency - US can inflate/soft default faster than world can unwind. And TBH US will probably be "fine" as long as US can still gunboat diplomacy. If can't be banker anymore, be the mob boss.