[tialaramex]

It's a power Kings have. "The Royal Prerogative of Mercy". That's why the President has it, there weren't a lot of other examples for the Executive to be modelled on. However of course in modern constitutional monarchies the King doesn't operate this power any more, for example Liz's pardon power is operated by her government and ordinarily via some dusty committee looking into injustices (the government occasionally has used it directly e.g. some guy years into his life sentence for murder tackled a terrorist who was stabbing people at an event in London, the Pardon power was used to reduce his sentence in recognition of this bravery)

The US President should have handed this power over to a similarly dusty committee resolving real injustice years ago. This would be less corrupting and more effective because a President is busy whereas the committee would be doing nothing else except investigating the circumstances of potential injustice and choosing how to resolve them (new trial, pardon, etc.)