The reason they hate this pardon so much is that they want to deny Trump any of the powers of the Presidency, with their deep state leaks and their investigations and their Rino critiques, and inability to pass legislation. When he refusts to accept the box they are trying to put him in, it really makes them mad. When he’s a good boy and lets them keep wasting lives and money in Afghanistan, they pat him on the head. The pardon required he be reminded he’s not really President.
This is just part of the 24/7/365 game of rotating attacks on Trump; tomorrow a few other libs in different parts of the country will attack Trump for other issues, all implying he is 1) unfit, and 2) breaking the law. This cycle will continue throughout his term; the logic is if they peal off one voter with each story eventually 100 million stories should do the trick...