Yes, we all know about Lord Acton’s famous aphorism. But power doesn’t just corrupt the person who wields it, it also corrupts those who observe power in action.
Power causes outside observers to adjust their views in such a way as to make the most powerful men seem more virtuous. When an outsider criticizes a powerful man, many people will naturally gravitate in support of the powerful man, even if their actual views would suggest more sympathy for the attacker. (Perhaps this is true of powerful women as well, I am less sure of that claim.)
Most conservatives have outlooks and personalities more aligned with people like Bolton, Sessions, Mattis, Tillerson, Kelly etc. than with Donald Trump. But when Trump is attacked, they instinctively believe that the attacker is lying, and that Trump is an innocent victim.
Most importantly, they do not reach this conclusion due to any sort of objective information—indeed all the evidence points in the opposite direction. Rather Trump’s power subtly warps their minds, causing them to believe things that are obviously not true.
Of course the Democrats have exactly the opposite reaction. However theirs is more justifiable (in this case) precisely because all the objective information suggests the attackers are correct. The Democrats don’t like the politics of the attackers, but never doubted that they are more honest men than Trump.
American presidents have far too much power, and the corruption I describe is just one of the many bad consequences of the imperial presidency.
The ideal is a bland president like Coolidge, and Biden is a bit closer to that ideal than Trump.