His biggest blunder, which we'll be paying for for years to come, is the total lost of institutional memory that's happened across the board under his administration.
Firing/losing/eliminating leading positions in the state department particularly, but most glaringly... basically closing the whitehouses pandemic response office by failing to replace it's leadership back in 2018.
Did Trump Administration Fire the US Pandemic Response Team?
His relentless attack on "Deep State" is eliminating apolitical civil servants that performed crucial functions. Some of which he crammed ignorant sycophants into, many of which he just left empty.
Gotta pay for those tax breaks for the rich some how... And hey, if government can't function, that's great for corporate profits, right?
*GRUMBLE* .... it's one thing to sit around doing nothing... it's another to basically tear down the entire executive branch along with you.
The orange baboon is a traitor to his country.