Chuck Hagel Kevin Lamarque - Reuters The dismissal of Barack Obama's Defense Secretary, Chuck Hagel, marks yet another instance in which the President and his closest aides find themselves at odds with senior colleagues primarily on the issue of Syria.

Hagel's departure is openly acknowledged in Washington to have been more of a sacking than a resignation, and directly linked to disputes regarding Syria policy.

Specifically, Hagel's departure is linked directly to a highly critical two-page memo on Syria policy he addressed to National Security Advisor Susan Rice that was leaked last month.

At the time it was assumed that even though it was obvious that Hagel was addressing Obama indirectly by seeming to address Rice — the closeness of the two both personally and on policy issues being an administration byword — the memo fell into the category of permissible dissent because Syria policy was under construction. Over the medium term, however, it appears that Hagel went too far, and has been perceived as directly challenging the President. The memo is typically described as "sharply critical."

The nature of the dispute is highly significant.

According to the leaked memo, Hagel had two main concerns about the administration's approach to Syria policy.

First, he argued strongly that the US States needs to be much clearer about its position on the future of Syrian dictator Bashar al-Assad. The studied ambiguity of the current policy regarding Assad, he argued, stands to "unravel" the American effort to "degrade and ultimately destroy" the Islamic State group (ISIS) in Iraq and Syria.

Hagel reportedly strongly urged the administration to clarify that it isn't simply going to refuse to get into an open alliance with Assad, but that it is prepared to begin to take actions, as well as introducing much more rhetorical clarity, that leave no doubt that the US is both seeking and pursuing regime change in Syria.

Without that, Hagel apparently argued, the campaign against the Islamist extremists would run up against insurmountable obstacles because it would be perceived as benefiting the dictatorship and, therefore, being fundamentally inimical to the core interests of the Sunni Arab populations that ISIS both rules and claims to represent, particularly in Syria.

In ongoing administration disputes beyond his highly critical memo, Hagel has also strongly urged a greatly expanded campaign to arm, train and finance moderate opposition forces that could simultaneously serve as an alternative to ISIS and press the battle in Syria against the dictatorship. On both counts its efforts would be essential.

ISIS fighters Screenshot/http://www.pbs.org/wgbh/pages/frontline/rise-of-isis/ If there is no alternative to ISIS’ fighters, they will continue to be able to command unwarranted and unearned support from angry and desperate Sunni communities that have faced a regime that has had no compunction in using all forms of conventional firepower, as well as chemical weapons, to dispense with at least 200,000 of its own citizens in the past three years.

And if those same communities conclude that the anti-ISIS coalition effort either wittingly or unwittingly benefits that regime, rather than stands as a new challenge against it, there is no way for them to embrace the effort. To the contrary, as Obama himself recently noted, such an impression would serve to drive Sunni Arabs in Syria toward ISIS, however reluctantly, and away from any support for the coalition's efforts.

A Growing List Of Frustrated Former Staffers

Hagel therefore joins the distinguished and growing list of former administration officials deeply connected to Syria policy who have openly expressed their frustration at the Obama approach. Numerous former officials including former Secretary of State Hillary Clinton, former CIA director David Petraeus, former Defense Secretary Leon Panetta, former special advisor for transition in Syria Frederic Hof, and many others are on record as not only disagreeing with administration policy on Syria, but identifying some of it as part of the problem.

In August 2012, Petraeus presented a plan to the administration for greatly intensified arming and training of moderate rebel forces in Syria. The plan was supported by Clinton and Panetta, as well as the chairman of the Joint Chiefs of Staff, Martin Dempsey. But it was strongly opposed by Rice and others, and ultimately rejected by Obama.

Given that she almost certainly has ongoing political ambitions of her own, Hillary Clinton has, perhaps, been notably forthright. In August, she observed that, “The failure to help build up a credible fighting force of the people who were the originators of the protests against Assad — there were Islamists, there were secularists, there was everything in the middle — the failure to do that left a big vacuum, which the jihadists have now filled.”

In October at Harvard University, Vice President Joe Biden offered an alternate, although somewhat incoherent, theory explaining the rise of ISIS:

Our allies in the region were our largest problem in Syria. The Turks were great friends and I have a great relationship with Erdogan, which I just spent a lot of time with. The Saudis, the Emirates, etc. What were they doing? They were so determined to take down Assad and essentially have a... Sunni/Shia war. What did they do? They poured hundreds of millions of dollars and tens of thousands of tons of weapons into anyone who would fight against Assad. Except that the people who were being supplied were Al-Nusra, and Al-Qaeda and the extremist elements of jihadis coming from other parts of the world.

Even if Biden is correct that some US allies, such as Turkey, were involved in the rise of ISIS through either acts of omission or commission, or both, Clinton's indictment of administration policy still stands. The former Secretary of State was describing the vacuum that policy created.

U.S. Vice President Joe Biden (L) meets with Turkey's President Tayyip Erdogan at Beylerbeyi Palace in Istanbul November 22, 2014. REUTERS/Murad Sezer The Vice President was presenting an interpretation of who and what filled the vacuum once it opened. It's noteworthy that Biden had to apologize to Turkey, Saudi Arabia and the UAE for those remarks, while Clinton hasn't apologized to anybody and isn't going to.

Was Hagel offering a kind of policy synthesis resolving this thesis and antithesis regarding the rise of ISIS?

If so, it wasn't appreciated and it certainly hasn't been accepted. To the contrary, it has resulted in his dismissal. But the fundamental contradiction that Hagel has identified — that the battle against ISIS cannot be won as long as US policy towards Assad remains ambiguous and ambivalent — remains unavoidable.

As I've written many times in the past, the inescapable bottom line is that the administration will ultimately have to choose between presiding over a campaign against ISIS that achieves much less than the stated "degrade and ultimately destroy" goal, or finally biting the bullet and making regime change in Syria an inextricable part of the American project.

Getting rid of people who irksomely point this out isn't going to alter an equation, like this one, that is hardwired into the reality of the problem.

Hussein Ibish is a columnist at NOW and The National (UAE). He is also a senior fellow at the American Task Force on Palestine. He tweets @Ibishblog