What's the historical reason the president even has this power?
Historically, it is a method for the rulers to build better relations with ordinary people by pardoning convictions that were popularly seen as unjust. In the US in particular, the pardon has historically been more heavily used by left-wing/progressive presidents in order to address legitimate injustices. Modern Republicans have used the pardon sparringly, particularly since the War on Drugs shifted perceptions about crime in the country.
The pardon is thus historically an acknowledgment that the justice system is flawed and there are innocent people who get convicted of crimes or people are unduly punished for minor crimes. The pardon gives those people an avenue to seek relief from that injustice.
The biggest issue with the pardon in the US is that it isn't used enough to address the massive issues in unjust sentencing in this country. Those problems need more fundamental changes to fix, but the pardon could be used to offer some more immediate help.
The best solution to a man like Trump having the pardon is to just not let him be President in the first place. If the people who make the rules are corrupt, no amount of rules will stop them.
www.reuters.com
