I don't think John Brennan's political stance obligates the US government to maintain his security clearance. How the President feels about John Brennan's political stance doesn't obligate the US Government to maintain his security clearance. I understand you are pissed John Brennan got his wee-wee caught in his zipper trying to have a pissing contest with the President. The utter ignorance in that would suggest it might not be a good idea to trust him with sensitive material.
Trump's actions are those of a vindictive president who is incapable of responding to critics other than attacking them.
Taking clearances away from former Intelligence people does not silence them nor damage them in any way. The clearance is not so much a benefit to the person. It’s more of a benefit to the particular government officials that would need some insight from times prior to them taking office. A person with a security clearance after leaving office doesn’t necessarily have access to any classified information unless a current agency requests it because access is on a need to know basis.
In other words, removing security clearances from former top intelligence officials creates a potential problem for the Intelligence community while giving these people a stronger voice to attack the president's policies. 
What's wrong with attacking your critics? It seems like the best strategy to me. Your theory that he should stand there and take it is absurd.
Revoking Brennan's security clearance is no problem for the intelligence community. He's a traitor who will never be asked for his advice or input on any matter whatsoever. His rants in the media have demonstrated beyond all doubt that his advice is idiotic and worthless
There is nothing wrong with attacking political opponents on issues. There is a lot wrong with personal attacks. Substituting crass personal attacks for sound political argument may win the approval of ardent supporters but it will loose support of others.
Taking the STFU route may work well in a campaign because a campaign is a zero sum game. You either win or you lose-. However, governing is never a zero sum game; you never get total victory. You have to appeal to those who aren't your supporters.
This is exactly the problem Trump has now. He needs support from a lot of people in his party and in the media that are not impressed by his crude language, shouting matches, and personal attacks. Every time Trump or his policies are attacked and he responds in this way he squanders the opportunity to increase his support.
Trump doesn't care. I think he wants to be impeached, the ultimate attention getter.
Time after time, Trump makes some really stupid statements, really dumb decisions, and he spends hours coming up with moronic, infantile, vindictive tweets that feed his many obsessions. It does no good for the media to focus on these. Actually, it does a great deal of harm.
How many times have we heard the media say Trump has "doubled down" on some foolish decision, some foolish tweet? That's because, if he has something that really pisses off the media, he will "double down" making it even more foolish. He does this because all the media attention feeds his monster super ego
and he is enjoying it.
You can tell he is enjoying himself because of his facial expressions and his demeanor. He loves the attention.
It is incomprehensible that a President would offer his opinion of an ongoing trial. What does Trump do? He tells a national television audience that Manafort is a really nice guy and his trial is a disgrace. Trump loves the attention that one got.
He got a tremendous amount of attention when he revoked Brennan's security clearance, nearly all of it negative. What does Trump do? He says he will probably do the same with nine other critics of his administration. Trump absolutely loves all the attention he got with that announcement.
Mueller really does not care if Trump refuses to present his side of the Russian probe, and no way will he get involved in litigation concerning a subpoena that will last until Christmas, Christmas of '19. Trump and his lawyer, Giuliani, have been making hay of this non-controversy for months. They argue against themselves and change their stories much to the delight of an American audience. And much to the delight of an audience of one in the Oval Office. Trump absolutely loves it.
I could go on all day, but the reader gets my point. When Trump issues a statement, makes a decision, writes a tweet, the more un-Presidential it is, the more controversial it is, the more anal-retentive it is, the more ill-advised it is the better. The longer the controversy goes on the better.
That is because, if the media is talking about something he did or said that was incomprehensibly stupid, then they are not talking about his collaboration with Russia during the 2016 election.
