The US Treasury Market

It is hard to make sense of Treasury yields using traditional models of risk and return without invoking something like a "convenience yield" that reflects the special role of the US dollar and US Treasury securities in the global financial system.

Demand curves slope down. Thus, a rightward shift in demand either increases quantity or raises price (lowers rate) depending on supply. It seems to me supply has shifted out to the point of greater quantity but not much lower rate.

Foreign investors hold about one third of US Treasuries (TIC data). With no foreign demand, then domestic US investors would therefore need to hold 50% more. Domestic Treasuries investors are far from inelastic (Jansen, Li and Schmid), and yields would need to rise a lot!
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Higher demand implies higher prices (lower yields). The trade deficit leads other countries to buy US treasuries. There is some uncertainty over what "substantial" means.
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Any policies to make it less convenient for foreign institutions to hold Treasuries will raise the yield. Speech below completely confuses the myriad benefits the US gets from being the reserve currency.
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The US has an exceptionally high demand from foreigners for its most liquid safe dollar debt. High demand does push bond prices up and interest rates down

There is evidence that foreign safe asset demand contributes to the convenience yield of Treasurys (Jiang, Z., Krishnamurthy, A. and Lustig, H., 2018, May. Foreign safe asset demand for US treasurys and the dollar. AEA Papers and Proceedings).

I am not sure about the substantially but it contributes to lower interest rates.

foreigners have fairly inelastic demand for US Treasuries relative to other investors
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I agree that macroeconomic fears (of inflation on the one hand, and a recession on the other) are primary - although technical factors (unwinding of the Treasury basis trade) likely also play an important secondary role.

Well, nobody can really know why a market price moves - see Hayek. And sometimes there are short-lived "plumbing" issues. But my guess is that we are at last seeing the long-anticipated loss of faith in US fiscal institutions that lowers foreign demand for dollar & treasury debt

The largest recent macro-fundamental shocks are successive large changes in US government tariff plans and foreign responses. These have driven up volatility in yields (by about 50%), equity returns (VIX roughly doubled), and FX returns.

Degraded macroeconomic prospects: 1) primarily driven by large tax increase (tariffs); 2. Concern that inflation could rise again; 3. The challenge to the safe haven status of the US$ and treasuries leads to higher rates further increasing the alarming US debt service cost.

Attacking the Fed and generating huge policy uncertainty has hurt stocks, the dollar and raised rates. But some of the fragility in the treasury market is due to the demands from asset managers and the reliance on levered investors to clear the market.
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Hard to say without serious empirical analysis of the current episode. One worries that US policymakers are introducing uncertainty about basic policies and this might result in a persistent re-evaluation of dollar assets safety

And policy uncertainty and global uncertainty.

Aside from the (policy-induced) macro uncertainty there are a number of additional sources of uncertainty about fiscal policy and the trustworthiness of the US as a borrower that are likely also contributing to Treasury volatility

other factors are at play too. If the Us president can easily upend the world order and easily change his mind every day, and if he threatens the independence of the FED or others, markets will not have a framework to form expectations. If randomness prevails, volatility will too

There are other factors as well.

very adverse fiscal news of $5trillion spending bill over 10 years moving forward in House and Senate subcommittees. Turns off all buyers, including and maybe more so foreigners. Amplified by unwind of the Treasury basis trade.