Arkin's 2,228-word memo to his colleagues says that his time at NBC News has been "gratifying." But he bluntly expresses his displeasure with the "Trump circus," US foreign policy failures, and the state of television news.

"In our day-to-day whirlwind and hostage status as prisoners of Donald Trump, I think — like everyone else does — that we miss so much," Arkin says.

He's far from the only person in a national newsroom to feel that way. But he is spelling it out in no uncertain terms.

Arkin has worked for NBC on and off for three decades, sometimes as a military analyst, sometimes as a reporter and consultant. He describes himself as a scholar at heart, and he has authored numerous books about national security, most recently "Unmanned," subtitled "drones, data, and the illusion of perfect warfare."

Friday will be his last day at NBC, according to his internal memo on Wednesday. It was shared with CNN by one of the recipients, and NBC confirmed its authenticity.

The network had no comment on his departure.

Arkin is a sharp critic of what he calls "perpetual war" and the "creeping fascism of homeland security."

Military analyst William Arkin speaks during a taping of 'Meet the Press' at the NBC studios December 12, 2004 in Washington, DC. Arkin joined a roundtable discussion on the current situation of the war in Iraq.

In his farewell memo, he said the American press is not aggressive enough about covering military engagements.

"I find it disheartening that we do not report the failures of the generals and national security leaders," he said. "I find it shocking that we essentially condone continued American bumbling in the Middle East and now Africa through our ho-hum reporting."

He said that most of his critiques of NBC apply to the rest of the news media, as well.

Years ago, he said, "particularly as the social media wave began, it was clear that NBC (like the rest of the news media) could no longer keep up with the world. Added to that was the intellectual challenge of how to report our new kind of wars when there were no real fronts and no actual measures of success."

Arkin is inclined to agree with some of Trump's isolationist instincts, though he called Trump an "ignorant and incompetent impostor."

"And yet," he wrote, "I'm alarmed at how quick NBC is to mechanically argue the contrary, to be in favor of policies that just spell more conflict and more war."

Staffers at NBC might object to that line — pointing out that the network doesn't take an institutional position in favor of any policy. But Arkin is describing the impression he takes away from the news coverage and commentary.

He also said in the memo that the Trump age led NBC to start "emulating the national security state itself — busy and profitable. No wars won but the ball is kept in play."

In the memo, Arkin called himself a "difficult guy," and gave NBC a lot of credit for keeping him in the corporate family for so long.

He said he is leaving because his expertise, "though seeming to be all the more central to the challenges and dangers we face, also seems to be less valued at the moment. And I find myself completely out of synch with the network, being neither a day-to-day reporter nor interested in the Trump circus." He is working on multiple books and other projects.

Here is the full text of Arkin's memo.

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January 4 is my last day at NBC News and I'd like to say goodbye to my friends, hopefully not for good. This isn't the first time I've left NBC, but this time the parting is more bittersweet, the world and the state of journalism in tandem crisis. My expertise, though seeming to be all the more central to the challenges and dangers we face, also seems to be less valued at the moment. And I find myself completely out of synch with the network, being neither a day-to-day reporter nor interested in the Trump circus.

I first started my association with NBC 30 years ago, feeding Cold War stories to Bob Windrem and Fred Francis at the Pentagon. I became an on-air analyst during the 1999 Kosovo War, continuing to work thereafter with Nightly News, delighting and oftentimes annoying in my peculiar position of being a mere civilian amongst THE GENERALS and former government officials. A scholar at heart, I also found myself an often lone voice that was anti-nuclear and even anti-military, anti-military for me meaning opinionated but also highly knowledgeable, somewhat akin to a movie critic, loving my subject but also not shy about making judgements regarding the flops and the losers.

When the attacks of 9/11 came, I was called back to NBC. I spent weeks on and off the air talking about al Qaeda and the various wars we were rushing into, arguing that airpower and drones would be the centerpiece not troops. In the new martial environment where only one war cry was sanctioned I was out of sync then as well. I retreated somewhat to writing a column for the Los Angeles Times, but even there I had to fight editors who couldn't believe that there would be a war in Iraq. And I spoke up about the absence of any sort of strategy for actually defeating terrorism, annoying the increasing gaggles of those who seemed to accept that a state of perpetual war was a necessity.

I thought then that there was great danger in the embrace of process and officialdom over values and public longing, and I wrote about the increasing power of the national security community. Long before Trump and "deep state" became an expression, I produced one ginormous investigation -- Top Secret America -- for the Washington Post and I wrote a nasty book -- American Coup -- about the creeping fascism of homeland security.

Looking back now they were both harbingers for what President Obama (and then Trump) faced in terms of largely failing to make enduring change.

Somewhere in all of that, and particularly as the social media wave began, it was clear that NBC (like the rest of the news media) could no longer keep up with the world. Added to that was the intellectual challenge of how to report our new kind of wars when there were no real fronts and no actual measures of success. To me there is also a larger problem: though they produce nothing that resembles actual safety and security, the national security leaders and generals we have are allowed to do their thing unmolested. Despite being at "war," no great wartime leaders or visionaries are emerging. There is not a soul in Washington who can say that they have won or stopped any conflict. And though there might be the beloved perfumed princes in the form of the Petraeus' and Wes Clarks', or the so-called warrior monks like Mattis and McMaster, we've had more than a generation of national security leaders who sadly and fraudulently have done little of consequence. And yet we (and others) embrace them, even the highly partisan formers who masquerade as "analysts". We do so ignoring the empirical truth of what they have wrought: There is not one county in the Middle East that is safer today than it was 18 years ago. Indeed the world becomes ever more polarized and dangerous.

As perpetual war has become accepted as a given in our lives, I'm proud to say that I've never deviated in my argument at NBC (or at my newspaper gigs) that terrorists will never be defeated until we better understand why they are driven to fighting. And I have maintained my central view that airpower (in its broadest sense including space and cyber) is not just the future but the enabler and the tool of war today.

Seeking refuge in its political horse race roots, NBC (and others) meanwhile report the story of war as one of Rumsfeld vs. the Generals, as Wolfowitz vs. Shinseki, as the CIA vs. Cheney, as the bad torturers vs. the more refined, about numbers of troops and number of deaths, and even then Obama vs. the Congress, poor Obama who couldn't close Guantanamo or reduce nuclear weapons or stand up to Putin because it was just so difficult. We have contributed to turning the world national security into this sort of political story. I find it disheartening that we do not report the failures of the generals and national security leaders. I find it shocking that we essentially condone continued American bumbling in the Middle East and now Africa through our ho-hum reporting.

I'm a difficult guy, not prone to either protocol or procedure and I give NBC credit that it tolerated me through my various incarnations. I hope people will say in the early days that I made Brokaw and company smarter about nuclear weapons, about airpower, and even about al Qaeda. And I'm proud to say that I also was one of the few to report that there weren't any WMD in Iraq and remember fondly presenting that conclusion to an incredulous NBC editorial board. I argued endlessly with MSNBC about all things national security for years, doing the daily blah, blah, blah in Secaucus, but also poking at the conventional wisdom of everyone from Matthews to Hockenberry. And yet I feel like I've failed to convey this larger truth about the hopelessness of our way of doing things, especially disheartened to watch NBC and much of the rest of the news media somehow become a defender of Washington and the system.

Windrem again convinced me to return to NBC to join the new investigative unit in the early days of the 2016 presidential campaign. I thought that the mission was to break through the machine of perpetual war acceptance and conventional wisdom to challenge Hillary Clinton's hawkishness. It was also an interesting moment at NBC because everyone was looking over their shoulder at Vice and other upstarts creeping up on the mainstream. But then Trump got elected and Investigations got sucked into the tweeting vortex, increasingly lost in a directionless adrenaline rush, the national security and political version of leading the broadcast with every snow storm. And I would assert that in many ways NBC just began emulating the national security state itself -- busy and profitable. No wars won but the ball is kept in play.

I'd argue that under Trump, the national security establishment not only hasn't missed a beat but indeed has gained dangerous strength. Now it is ever more autonomous and practically impervious to criticism. I'd also argue, ever so gingerly, that NBC has become somewhat lost in its own verve, proxies of boring moderation and conventional wisdom, defender of the government against Trump, cheerleader for open and subtle threat mongering, in love with procedure and protocol over all else (including results). I accept that there's a lot to report here, but I'm more worried about how much we are missing. Hence my desire to take a step back and think why so little changes with regard to America's wars.

I know it is characteristic of our overexcited moment to blast away at former employers and mainstream institutions, but all I can say is that despite many frustrations, my time at NBC has been gratifying. Working with Cynthia McFadden has been the experience of a lifetime. I've learned a ton about television from her and Kevin Monahan, the secret insider tricks of the trade and the very big picture of what makes for original stories (and how powerful they can be). The young reporters at NBC are also universally excellent. Thanks to Noah Oppenheim for his support of my contrarian and disruptive presence. And to Janelle Rodriguez, who supported deep expertise. The Nightly crew has also been a constant fan of my too long stories and a great team. I continue to marvel as Phil Griffin carries out his diabolical plan for the cable network to take over the world.

I'm proud of the work I've done with my team and know that there's more to do. But for now it's time to take a break. I'm ever so happy to return to writing and thinking without the officiousness of editorial tyrants or corporate standards. And of course I yearn to go back to my first love, which is writing boring reports about secret programs, grateful that the American government so graciously obliges in its constant supply. And I particularly feel like the world is moving so quickly that even in just the little national security world I inhabit, I need more time to sit back and think. And to replenish.

In our day-to-day whirlwind and hostage status as prisoners of Donald Trump, I think -- like everyone else does -- that we miss so much. People who don't understand the medium, or the pressures, loudly opine that it's corporate control or even worse, that it's partisan. Sometimes I quip in response to friends on the outside (and to government sources) that if they mean by the word partisan that it is New Yorkers and Washingtonians against the rest of the country then they are right.

For me I realized how out of step I was when I looked at Trump's various bumbling intuitions: his desire to improve relations with Russia, to denuclearize North Korea, to get out of the Middle East, to question why we are fighting in Africa, even in his attacks on the intelligence community and the FBI. Of course he is an ignorant and incompetent impostor. And yet I'm alarmed at how quick NBC is to mechanically argue the contrary, to be in favor of policies that just spell more conflict and more war. Really? We shouldn't get out Syria? We shouldn't go for the bold move of denuclearizing the Korean peninsula? Even on Russia, though we should be concerned about the brittleness of our democracy that it is so vulnerable to manipulation, do we really yearn for the Cold War? And don't even get me started with the FBI: What? We now lionize this historically destructive institution?

Even without Trump, our biggest challenge as we move forward is that we have become exhausted parents of our infant (and infantile) social media children. And because of the "cycle," we at NBC (and all others in the field of journalism) suffer from a really bad case of not being able to ever take a breath. We are a long way from resolving the rules of the road in this age, whether it be with regard to our personal conduct or anything related to hard news. I also don't think that we are on a straight line towards digital nirvana, that is, that all of this information will democratize and improve society. I sense that there is already smartphone and social media fatigue creeping across the land, and my guess is that nothing we currently see -- nothing that is snappy or chatty -- will solve our horrific challenges of information overload or the role (and nature) of journalism. AndI am sure that once Trump leaves center stage, society will have a gigantic media hangover. Thus for NBC -- and for everyone else -- there is challenge and opportunity ahead. I'd particularly like to think and write more about that.

There's a saying about consultants, that organizations hire them to hear exactly what they want to hear. I'm proud to say that NBC didn't do that when it came to me. Similarly I can say that I'm proud that I'm not guilty of giving my employers what they wanted. Still, the things this and most organizations fear most -- variability, disturbance, difference -- those things that are also the primary drivers of creativity -- are not really the things that I see valued in the reporting ranks.

I'm happy to go back to writing and commentary. This winter, I'm proud to say that I've put the finishing touches on a 9/11 conspiracy novel that I've been toiling on for over a decade. It's a novel, but it meditates on the question of how to understand terrorists in a different way. And I'm undertaking two new book-writing projects, one fiction about a lone reporter and his magical source that hopes to delve into secrecy and the nature of television. And, If you read this far, I am writing a non-fiction book, an extended essay about national security and why we never seem to end our now perpetual state of war. There is lots of media critique out there, tons of analysis of leadership and the Presidency. But on the state of our national security? Not so much. Hopefully I will find myself thinking beyond the current fire and fury and actually suggest a viable alternative. Wish me luck.