With the resignation/termination of James Mattis as defense secretary, President Trump’s love affair with generals has seemingly run its course. Of course, with Trump affairs of the heart tend to be transient rather than lasting. So this latest breakup does not exactly come as a surprise.

In this instance, the impetus for the split appears to be this: Mattis, along with former White House chief of staff General John Kelly and former national security adviser Lieutenant General H.R. McMaster, displeased their boss big time. Simply put, the officers that Trump once proudly referred to as “his” generals didn’t follow his orders.

Devoid of prior experience in either government or the military, Trump radically misconstrued the role of commander-in-chief. The title itself is a grand one, suggesting that the bearer makes decisions (Remember George W. Bush:  “I am the decider.”), to which subordinates respond by briskly saluting, making an about face, and marching off to do precisely what they’ve been told to do.

As Trump has discovered, very much to his frustration, that’s not the way the civil-military relationship actually works. While enthusiasm may greet some presidential national security-related actions—calls to increase military spending, for example—others can induce resistance. Smart presidents minimize resistance by making sure that senior officers are onboard before announcing a decision. Less smart presidents—recall, for example, Bill Clinton’s abortive efforts to allow gays to serve openly in the armed forces— find themselves obliged to back down.

Trump got a glimpse of this reality early on when he ordered the Pentagon to organize a parade to display and celebrate American military might. Mattis decided that the troops had better things to do and quietly scuttled the idea.

Trump seems to have learned nothing from that episode. For someone who prides himself on being a dealmaker, he has demonstrated little aptitude for negotiating with nominally subordinate generals and admirals.

Further complicating Trump’s problem is his rejection of the worldview to which senior military officers, along with the rest of the permanent national security apparatus, subscribe. Trump professes to believe in “America First.” Mattis, Kelly, and McMaster and other members of the brass believe in “global leadership,” which implies (among other things) gargantuan Pentagon budgets, a vast network of bases, suitably compliant allies who provide markets for American arms, and—a recent codicil—a willingness to fight very long wars even when those wars prove unwinnable and pointless.

Now injecting the phrase “America First” into any discussion of foreign policy is a bit like suggesting that the NAACP adopt “Dixie” as its official anthem. Doing so makes meaningful conversation all but impossible.

So while, Trump has used “America First” effectively to rally his supporters, he has yet to translate the phrase into anything approximating a coherent approach to policy to which the establishment might give its assent. The National Security Strategy drafted under McMaster’s supervision—a document that Trump may not have read and certainly never embraced—was dead on arrival. In reality, the United States today has nothing that qualifies as a national security strategy. What we have is a set of old habits, many of them obsolete, that are undermined by random presidential tweets, which may or may not result in any follow-up. It makes for quite a spectacle.

There is an intellectual void at the center of this administration. Never on the same page with their commander-in-chief, Trump’s generals proved unable to fill that void. Now that they are gone, the void assumes galactic proportions. The year 2019 promises to be an interesting one.

Andrew Bacevich is TAC’s writer-at large.