To answer this you have to consider the following:
There is unilateral agreement amongst intelligence services that Russia interfered in the US elections in 2016. Former president Jimmy Carter has denounced Trump calling him an illegitimate president. The Mueller investigation into Russian interference resulted in the poisonous conclusion that Trump could not be exonerated from the crimes of treason and collusion without a trial. Never before has the legitimacy of a president been called into question in this manner. The report also describes Trump's efforts to control the investigation which amount to obstruction of justice.
We have witnessed the depth of the rot through the jailing of Michael Cohen, Trump's former attorney convicted of tax fraud, campaign finance violations, and bank fraud.
His former campaign manager Paul Manafort has also been jailed for fraud. Former campaign staff Rick Gates and George Papadopoulos, and former US National Security Adviser Michael Flynn have all been charged in connection with the Mueller investigation. The whole affair has left Americans asking themselves some pretty heavy questions in relation to the sanctity of the White House and the criminals associated with this administration.
Is this the worst presidency in living memory?
Trump openly boasts about his assault on environmental laws, a sequence of roll backs which have been to the sole benefit of the fossil fuel industry. In the wake of a global environmental catastrophe America has become a leader in the destruction of the planet.
We're also witnessing an era of lawlessness that has caused fear and panic in the lives of ordinary Americans. Domestic terrorism is an American cancer, more people were murdered by far-right extremists in the US last year than in any other year since the Oklahoma City bombing in 1995. From Trump rhetoric "There are good people on both sides" to out right denial of gun violence this is a president who has no interest in protecting the lives of innocent men, women, and children.
The United States has become one of the five most dangerous places in the world to work as a journalist. At least 63 professional journalists were killed doing their jobs in 2018. When you look at the groups of people Trump attacks journalists immediately spring to mind. This is one of the worst periods of American history if you're an investigative journalist or if you want to ask the president hard questions, like Jim Acosta does.
The repeal of Universal Health Care is a crime against humanity. A wealthy country should be able to afford to take care of it's people. Again the interests of corporations have been put ahead of the interests of the American people.
Of course this era has been good for some people. Trump has raised the estate tax exemption under the Tax Cuts and Jobs Act to $11.18 million, meaning assets valued up to that amount can be transferred without triggering the 40 percent tax. In 2017, the exemption was $5.49 million per individual. Trump fully intends to eliminate the tax on wealth transfer altogether.
Trump's rhetoric has shocked America and his administration has been an attack on all that she values. From agitating racists to open abuse of the press his presidency will be remembered for being the most deplorable four years in modern American history.
Picture by Aaron Johnson, "The Burial of Liberty," 2016