So, if I understand it properly, your model of the world is that the USA needs to borrow in dollars (its own currency) in order to finance itself. In the case that there were not enough buyers for their bonds, the interest rate of the bonds should go up because offer and demand.
This beg the question of where is the money coming in the current situation, where all the major countries are following the same policies.
At the same time, you are saying that "foreign investors" and "governments" are buying bonds with negative inflation-adjusted profits because they have "faith" in the US economy. So, in the last years, at the same time the deficit and the public debt went up, the "faith" has gone up as show by the interest rate.
Here is an alternative view: the markets are powerless to determine the interest rate against the central bank. An example, Italy and the crisis of debt of 2011. They had a debt crisis until the ECB decided there will be not more crisis.
The markets dance to the song that the Fed sing. I don't know what more have to happens for people to start accepting it. The federal government don't need the markets, the markets need the bonds.