To a large degree, they aren't accepting it. This is why around 2014 treasury holdings by rest of world stopped growing on net.
Many governments/central banks are trying to exit the $ and UST's and are buying gold instead of treasuries.
Ultimately, the US has quite a large amount of liabilities, and entitlement spending on retiring boomers coming due in the next few years. Currently, at the peak of the economic cycle, we are running $trillion deficits.
Imagine what happens if there is a recession? Even if there isn't, these fiscal deficits, along with our large trade deficit mean:
The rest of the world gives us real goods, we give them paper IOU's. The debt is not shrinking but is growing, and faster.
So, they are not tolerating it. Problem is, in the petrodollar system, the reason this whole ponzi could occur is dollars were needed to buy oil. Post-71 Nixon shock, the $ was as good as oil. Saudi and others only sold oil for dollars putting a floor on the value of dollar and incentivizing both oil exporters and rest of world to want to hold dollars, thus recycling their surpluses into treasury debt to both fund their export economies and fund our consumption.
This CANNOT continue because by definition it means rest of world works and produces for never ending, and ever growing, US consumption. Holding dollars, amidst a growing realization the Fed would have to monetize this debt and government would never pay it back in "real terms" has led many oil exporters to try to sell oil in other currencies, and countries generally to try to exit the dollar for trade.
Iraq[0], Libya, Iran, Russia, and Venezuela[1]. Do we see a pattern of what happens to nations that try to do this?
They either get regime-changed or become enemy number one for US government. Do you think it is a coincidence that Venezuela has the largest oil reserves in the world and just happens to be the next country US is involved in pushing regime change (them or Iran)?
To read about this system of petrodollar recycling, and how/when it was created in the early 70's because of collapse of Bretton Woods, check out an this excerpt[3] from excellent book "The Global Minotaur: America, Europe and the Future of the Global Economy" by Yanis Varoufakas former Greek minister of finance.
Good thread [3] covering a broad summary of trade, the dollar, and petrodollar warfare [4]
[0] http://www.thirdworldtraveler.com/Iraq/Iraq_dollar_vs_euro.h...
[1] https://www.mintpressnews.com/petrodollar-warfare-the-common...
[3] https://www.yanisvaroufakis.eu/2011/02/10/surplus-recycling-...
[3] https://twitter.com/TheSuperbubble/status/109944882078459904...
[4] https://en.wikipedia.org/wiki/Petrodollar_warfare