Two things. First, the Fed chairs aren't acting merely within their mandates. Price stability and the impact of inflation continues to be under reported because of things like hedonics, "efficiency" and unequal weighting in price metrics. Said another way, inflation continues to run much hotter than the mandate because the Fed ignores the share of costs with things like food, health care and rent, and continues to think that, because dish washers have gotten 20% more efficient in the last 10 years, they've come down in price. So they're failing miserably on that.
Second, they can't really do much to drive the employment mandate because, as any one with an IQ over 80 can tell you, the Fed doesn't drive employment and it can't make companies hire more people. The so-called "pushing on a string" narrative.
Lastly, the driving up of asset prices (stocks, housing, etc) is not a mandate at all, but something the Fed's owner banks have found works well for them and the rich, and so this drives inequality as a good half of the country doesn't even have the money to get into the stock market.
So yeah, the Fed chairs have failed miserably and continue to push the same broken model, with the only answer being "well, if it didn't work we didn't do enough money printing". The problem is that the money isn't going to where it is needed. Why? Because the Fed has no way of doing it correctly.
Blame the Fed, and blame the Presidents putting the same clowns in office to do the same thing over and over again.