Washington (CNN) Gen. James Mattis' resignation triggered an outpouring of anxiety and anger and a steady stream of kudos for the 68-year-old, but as the shock of his departure begins to ebb, another narrative about the "warrior monk" is emerging.

Even as Mattis is being hailed as a "national treasure" and praised for his moral compass and "sound judgment," conversations with multiple US defense officials reflect a frustration with the outgoing defense secretary.

While some of these frustrations are being overshadowed by President Donald Trump's decision to push Mattis out of his post on January 1, two months earlier than originally planned, these sources suggest that the general's tetndency to exert tight control may have contributed to the crisis surrounding Trump's precipitous decision Wednesday to end the US military presence in Syria and scale it back in Afghanistan.

Mattis resigned in disagreement over Trump's Syria decision, which will likely empower Russia and Iran and leave Syrian Kurds -- staunch US allies -- at risk from both ISIS and Turkey. The Associated Press, citing US and Turkish officials, first reported that the President agreed to the withdrawal in a phone call with Turkish President Recep Tayyip Erdogan last week without consulting his national security team or US allies.

At odds for months

Mattis' resignation capped an extended period of tension with the President, though fundamental differences have long existed. Mattis is a 68-year-old who has devoted his life to the military. Trump, meanwhile, is a 72-year-old who is drawn to heroic military figures but repeatedly sidestepped the draft as a young man and, until earlier this month when he traveled to Iraq, had yet to make a customary presidential visit to troops in overseas combat zones.

Several administration officials tell CNN they believe that if, in fact, Mattis and Trump had been at odds for months, the secretary had an obligation to leave far earlier than he did. He waited too long to act and now, they say, the Kurds will pay the price.

These officials argue that if Mattis had left after Trump dismissively referred to him in an October interview with CBS' "60 Minutes" as "sort of a Democrat," there could have been another defense secretary in place who might have been able to talk the President out of the troop drawdown.

"Writing a formal letter and presenting it to the boss personally was exactly the right thing to do. It is very much in keeping with military custom.," said John Kirby, CNN's military and diplomatic affairs analyst and a retired rear admiral. But, he added, "Having that letter be so long and philosophical, reading almost as a manifesto of sorts, and then aggressively pushing it out to media outlets shortly after delivery came across as little more than a shot at redemption and a chance to get ahead of Trump's spin."

But Mattis is the same person he has always been, the officials said, none of whom are Trump supporters. They portray the secretary as driven by his own views and determination to stay on the job while trying to keep from angering Trump, and they add that the very public orchestration of his departure is not going down well in some military circles.

CNN has reached out to the Pentagon for comment.

A US defense official said Trump has pushed a bold agenda, which Mattis helped shape. He convinced Trump to launch a new Afghanistan and South Asia strategy calling for increased troop levels and more military autonomy, helped bring together a coalition to defeat ISIS, and was the first in the administration to call for increased defense spending by NATO members, the official said.

"The President was the only one elected and must execute his agenda. To do that, he needs people who share his point of view. When the secretary determined he was no longer well aligned with the President, he rendered his resignation," according to a US defense official. "There is a long list of former and current administration officials, lawmakers and others who try and have tried to convince the President to make different decisions, but President Trump is his own man. And so is Jim Mattis."

The Defense Department has posted Mattis' resignation letter on Facebook and on its website. Some see this as a disrespectful dig at the President. And multiple defense officials are eagerly backgrounding reporters, saying more officials will also resign although no Defense Department personnel have so far done so.

Indeed, a military official who regularly talks to Mattis called his letter "a dog whistle" to anyone in uniform but particularly for the general officer corps, which should consider it a signal to resign if they also have issues with Trump's policies.

While there's no sign at this point of any officer resignations, Brett McGurk -- the American envoy to the coalition to fight ISIS -- also resigned on Friday over Trump's decision to pull US forces out of Syria.

One defense official pointed to an essential part of Mattis' departure, saying the secretary's exit might be a relief for some.

Mattis restricted access to information and put a chill on members of the military services talking publicly. Some might be relieved to see him go if they are now freer to push publicly for their agendas, the official said.

Mattis also discouraged senior officers from interacting directly with the President, worried that Trump might suddenly issue them orders -- senior officers would have had no option but to do as Trump wished, according to a defense official.

Running out of steam

Senior battlefield commanders who have had a chance to meet with the President have been dismayed that he had no questions for them and showed a lack of interest, CNN can confirm.

Mattis' own strategy for dealing with Trump eventually ran out of runway. He avoided speaking publicly for fear of getting crosswise with Trump or being seen in contradiction. He also tried delaying tactics on issues such as the Syria withdrawal, which had been on the table all year.

Following Mattis' tenure, officials speculate that Trump is unlikely to turn to another retired general to become the next secretary of defense.

Two names that been thrown about to be the next defense secretary are Mark Esper, the Army secretary, and Deputy Secretary of Defense Patrick Shanahan, who has already been appointed as acting secretary.

It remains to be seen whether they fare any better than Mattis.