They thought they could, then the Ghost of Hayak was heard laughing from Coast to Coast.

MMT literally argues that the monetary/fiscal division is artificial, and that the only constraint on fiscal policy is the monetary impact of net spending in the context of whatever traditional “monetary” policy is pursued, when you operate in your own fiat.

There being a monetary impact of either net spending or traditional monetary policy is not a blow to MMT.

No, that’s never been the case. If it was, loose monetary policy to prevent incipient deflation (which is exactly causing inflation compared to the status quo ante) wouldn’t work (and, conversely, leaving the loose money policy engaged too long would lead to inflation, like it did after the brief COVID recession.)

The US having the ability to borrow in its own currency (which is closely related to the dollar being a global reserve currency, but slightly different) means that it always has the theoretical capacity to monetize the debt.