Explain themselves? Impeachment? Prison? Is that a joke?
The reason you don't understand the backlash is because you don't understand how this works.
Those were things that were at least theoretically possible in the pre-9/11 system. What Bush changed and Obama continued, was making it into a system with zero accountability. All the executive has to do is claim that they think someone's a terrorist, there is no court, no evidence required, no higher authority they answer to or that could hold them accountable. One, single person has total and complete authority to kill anyone in the world. And what al-Awlaki showed is that this applies even to US citizens.
Theoretically, if Trump wanted to, he could launch a drone strike on Ilhan Omar's house and the only obstacle would be the political backlash. Y'all simply do not appreciate the degree to which the executive acquired dictatorial power in the "post-9/11 world." Bush was just Trump but with literally 90% of the country supporting him. Trump has only gone further because of the groundwork Bush laid. The "emergency" powers from post 9/11 are still in place, they were never going away.
The president can ride his bike with no handlebars.