I think for most on this board, "the establishment" has been a relatively decent deal. Decent pay, benefits, retirement, etc.
There is an entire subsection of this country that has been more or less run over by the "establishment" over the past 30 years. Humans, on the whole, are good at sensing what's fair and what's not. And people have seen decades now of unfair behavior; of all the money and wealth flowing up, and nothing but poverty and pain coming down. Trump was able to tap into that demographic. Believe it or not, Bernie did something similar, albeit from a different angle (money and social programs for all!!!!). The DNC was able to shut down Bernie, but the RNC didn't (or couldn't) stop Trump. Combine all that with the competition being the most establishment candidate out there in Hillary Clinton, and that's how you ended up with Trump in the Oval Office.
Trump wanted to portray himself as slaying all the swamp demons. I have no doubt that, behind closed doors, he was beholden to the age-old Golden Rule as every other politician (as in, those who have the gold, make the rules). This blogger does a decent job of pointing out some of the promises that evaporated as soon as he was elected. Particularly how Trump's campaign website had three distinct bullet points about promises to eliminate medical monopolies, that were subsequently deleted within 15 minutes of the election being called for him in 2016.
Realistically though, he was in many ways over-powered by the swamp. He reportedly explored firing Dr. Fauci as our Covid response floundered, only to find that even as President, he didn't have the power to unilaterally remove him.
In his final days in office, he put forth an order to create a new job category for civil service (Schedule F) which would include all govt employees who were in "policy related" positions. Employees in these position would be able to be removed at the whim of the President. Critics decried it as something to be abused by the Executive Branch, and described a scenario of the the federal bureaucracy being packed with the President's patronage hires after every election, which granted, the power was there. More importantly though, Schedule F would give the executive branch some level of a check on the obscene level of power held by unelected bureaucrats. Your average swamp creature leans left, and we're at this strange point in our history where we have this bizarre, hugely powerful, yet unelected administrative state.
Schedule F got slow-rolled, and then quickly cancelled when Biden took office. It continues to be brought up in the press as something that would be "The End of Days" for American Civil Service, threatening national security, Mom's apple pie, and all kinds of other things. I hope it gains traction again at some point in the future.