The President, be it Trump or anyone else, should not have the power to fire the head of our national police force. That power should belong to Congress. The President should only have the power to request that Congress review an appointment and then vote to either reaffirm or remove that person.
My 2 cents
There is no Constitutional provision for national police or intelligence agencies. Probably could be a good idea, but the Founders wanted the States to have all the marbles so far as possible. They were having a hard time convincing the states to sign up.... they made all kinds of promises.
The general principle of separation of powers does solidly support your notion, alt. Nobody should be above the law... well, there is an issue about Congressional ethics and all the money being bandied about by Lobbyists, revolving-door regulators/regulated Corporate bigshots, and such.
The issue the Founders were grappling with was just this: How to create a government that would not become corrupt and abusive like the British colonial governments run by British carpetbaggers....schills for the British Corporates of the time.
Comey has a long career with both parties of playing the political games, working the ropes so to speak. He is absolutely unfit for public office, I don't care who fired him, it had to be done.
I think Trump was afraid to fire him, looking for some kind of cover, unsure he could pull it off without it being used as it has been against him. Trump knew Comey was a playa, and it shows tremendous courage on Trump's part that he did it.
J. Edgar Hoover had the dirt on all the politicians in his time, too. I remember watching TV drama stuff that made him out like Jesus the Crucified, the one who saves us all from all crooks.
I don't know how you can ever have national police organizations that cannot be weaponized politically.....
Our only real hope is to vote the bums out more regularly, making it an issue when candidates have corporate and/or banker backers. And never voting for anyone with big ideas about how to run the world.....
But yes, make the FBI chief term-limited to two years and nominated by congress, approved by the Senate, signed off on by the President..... and answerable to a oversight committee comprised of nominees proposed by a national Sheriff's organization which must be approved by a national board of boy scout civic badge holders, twelve selected by lottery.....
Like I said, I don't know how you could EVER have a non-politicized national police force.....