Why does our political system permit the continued operation of those that fail at their jobs?

It does. It's called elections.

1) Spectacular economy that began to employ massive numbers of minorities at legitimate jobs with real nongovernmental benefits for the first time in U.S. history;

2) Direct military and economic confrontation of China and North Korean 'saber rattling' then a renegotiation of trade deals that were harming our nation's interests;

3) Backing down Russia from incursions into Europe using military displays and sanctions;

4) The worldwide destruction of ISIS and the personal elimination of its chief Iranian architect after cutting off the terrorist funding for it by dissolving the 'nuclear deal' that foolishly unfroze Iranian assets;

5) The construction of an entirely new medical infrastructure to battle lethal virus outbreaks while keeping us in the 'lowest tear' of predicted American deaths from the 'first wave' of Covid-19, (medical experts describe this as 100,000-240,000 deaths);

6) Doing all of this while fending off daily personal slander, attacks on his family, (even on his young child by a 'Constitutional expert' failing to make her case for impeachment), fending off 'Russian hoaxes' attempting to invalidate his election, 'Me Too' mob rule movements attempting to destroy his marriage and reputation, farce 'impeachment' attempts for making Presidential phone calls, ceaseless demonization in the Press as a 'racist' or 'criminal' (for which 40 years in legitimate business with people of all races and backgrounds proves untrue), while they seek to inflame race-based hatred, rioting, looting, destruction of memorials and anarchy, and, of course, a seemingly endless string of 'Judases' selling him and their own country out for sweet heart book deals and other public bribes.

Which of these do you consider to be the most 'termination worthy' offenses?

Also, are you 'high' right now? 

It does. It's called elections.

They're called "elections".

And Trump's "failures" are more a matter of subjective opinion than rational objective fact.