As far as I can tell, Donald Trump is the first American president in my lifetime to be actively engaged in business while serving as President of the United States.  I have no memory of Eisenhower, Kennedy, Nixon, Ford, Carter, Reagan, George H.W. Bush, or George W. Bush starting and running businesses while occupying the Oval Office. It is true that Lincoln was a known agent of the railroads and that Grant's administration was corrupt, as other 19th century administrations might have been when the creation of a new nation offered so much to plunder to those with power.  

I doubt presidents and their administrations can avoid doing favors for campaign donors and friends, and these favors little doubt bring gratuities when the president and his appointees are out of office.  Clinton and Biden were perhaps the first truly corrupt American presidents in my lifetime.  It was perhaps Clinton who "legitimized" selling influence. This practice took off in the Biden regime as so much evidence shows. The practice has been legally legitimized by the failure of the Trump regime to prosecute despite the evidence on Hunter Biden's laptop, evidence we no longer hear about.

As President Trump has seemingly escalated the practice of using the Oval Office for personal enrichment, prosecuting past offenders would be self-indicting. We can expect Biden and his son to walk free.

Trump confronts us with a broader issue. A number of articles have pointed out that Trump is using his presidency to enrich himself and his family. For example, an article in The New Yorker ( https://www.newyorker.com/news/a-reporter-at-large/trumps-profiteering-hits-four-billion-dollars?_sp=570500f4-1879-400d-a672-4a31a437ab22.1779115729475 ) reports that Trump has invested in companies that are competing for federal government permits and funding, has filed personal multi-billion dollar lawsuits against banks that are regulated by the Trump regime, which encourages the banks to settle, leases his name to resort hotels and golf courses, and suggests that Trump sold pardons, the net result being an increase in Trump's net worth of $4 billion, perhaps making Trump a billionaire for the first time. https://www.washingtonpost.com/archive/politics/1992/11/29/trump-went-broke-but-stayed-on-top/e1685555-1de7-400c-99a8-9cd9c0bca9fe/