Covering Washington during the Trump administration is a gloomy business. But Tuesday was a rare day for good cheer. Tuesday was the day that John Bolton stepped down as President Trump's national security adviser.

All Americans, and many millions of people around the world, should consider themselves fortunate that in the 17 months he served as Donald Trump's NSA, Bolton failed to realize what is always his foremost wish: to start a war. It wasn't for lack of trying — in Venezuela, in Iran, in North Korea. But for whatever reason, the effort did not succeed, and now this man most famous for one-dimensional thinking about international affairs — for whom diplomacy is for suckers and the threat of military force is the only tool rattling around in an otherwise empty toolbox — has left the White House. Let's hope he spends the rest of his days doing nothing worse than drawing a handsome paycheck from the Mujahedeen Khalq (MEK), the fringe group of Iranian dissidents and terrorists that lobbies hard in Washington for American military might to overthrow the government in Tehran and put the group in charge in its place.

Bolton's departure gives us an opportunity to reflect on what, and who, should follow him at the highest levels of foreign policymaking in the Trump administration. The answer is less obvious than it should be. That's because the Republican Party — and establishment thinking in the nation's capital more broadly — is in a greater state of flux on questions of international affairs than it has been in several decades. And Trump himself is a big part of the reason why.

To see how, it's important to grasp the state of foreign policy thinking prior to the launch of Trump's 2016 presidential campaign.

Disagreements about foreign policy in the nation's capital take place across three dimensions. On one dimension, realists do battle with moralists; on a second, aggressors square off against restrainers; on a third, unilateralists clash with multilateralists. The neoconservatives who receive so much attention in the press are unilateral aggressive moralists: They believe in using military might to spread American ideals across the globe, and that doing so is beneficial to every person of good will on the planet. They obviously favored this in Iraq in 2003, but neocons have used the same rationale to justify and advocate a wide range of other hawkish policies down through the years.

The liberal internationalists who shamed Bill Clinton for not intervening to stop the Rwandan genocide, who pushed him to take a stand against Serbia's actions in the former Yugoslavia, who went along with the Iraq War, and who convinced Barack Obama to topple the government of Muammar Gaddafi in Libya — I'm looking at you Hillary Clinton, Susan Rice, and Samantha Power — are also aggressive moralists who meaningfully differ from the neocons only in their preference for acting in concert with allies, ideally through large multilateral organizations. (The UN is best of all, but NATO will do.)

Bolton belongs in neither camp. He believes moral ideals have no place in crafting and enacting foreign policy. His only concern is advancing American interests as he understands them using force and the threat of force, full stop. That makes him a very aggressive unilateral realist.

It was easy to mistake Bolton for a neocon back during the administration of George W. Bush because the years immediately following the September 11 attacks were a boom time for squishy, feel-good tautologies in which otherwise intelligent people convinced themselves that all good things go together. The U.S. pursuing its good at the barrel of a gun harmonized perfectly with the good of the West as a whole, with Israel's good, and with the good of the Muslim Middle East, South Asia, and even the entire rest of the world (except for a few nihilistic, evildoing terrorists who would soon be wiped out with righteous American bombs). As Bush put it in his second inaugural address, "America's vital interests and our deepest beliefs are now one." In the dim light of such bromides, it was hard to tell the difference between aggressive realists like Bolton and Dick Cheney and aggressive moralists like neocons Paul Wolfowitz and Robert Kagan.

From the run-up to the Iraq War through almost the entirety of the Obama administration, Republicans kept up something very close to a united front of full-spectrum hawkishness. It was aggressive unilateralist moralists and realists standing shoulder to shoulder as far as the eye could see.

At least until Trump.

The real estate mogul and reality TV star shook the GOP to its foundations in multiple respects, but he was especially destabilizing in foreign policy. Here was a guy standing on a GOP debate stage during the 2016 primaries, facing a dozen rivals repeating shopworn über-hawkish talking points, and he had the gall to label the Iraq War a horrible mistake. There was almost an audible sigh of relief — and maybe even a few cheers —among Republican voters when he did so. Finally, someone was willing to admit a truth that was obvious to everyone: Bush had screwed up massively in Iraq, and the GOP's refusal to admit it ensured that his mistakes would be repeated again.

Now, that doesn't mean that candidate Trump really knew what he was doing or wanted to do in foreign policy. He knew and knows next to nothing about the world outside the United States. He's pathologically self-absorbed. He views life as an endless, ruthless competition among rivals. He's intensely skeptical of those who profess to be moved by selflessness. He thinks in terms of transactions and zero-sum negotiations.

Yet oddly enough, this cluster of character traits makes Trump a sort of untutored, instinctual realist by default — albeit one who favors military restraint instead of aggression. He has no interest at all in using American military might to spread democracy, to engage in nation building, or even to uphold the "liberal international order." That means he's no neocon. But he is equally uninterested in allowing our national interests to get us enmeshed in foreign conflicts that will draw us in for years or decades to come. Which means he's also not a Bolton-style aggressive realist. (Like nearly all Republicans, however, Trump is an unapologetic unilateralist.)

Trump's inchoate realism and relative restraint is, once again, purely instinctual. That, along with the president's erratic temperament, makes it unstable and uncertain. Add in the enormous hostility to restrained realism among members of the bipartisan foreign policy establishment in Washington, and you begin to grasp the source of the Trump administration's halting moves on the world stage. Trump doesn't even know enough to have a rudimentary sense of who he should hire (and avoid hiring) to help him enact the policies his impulses lead him to favor.

Bolton was a terrible choice. Let's hope Trump manages to do better in hiring a successor. Among academics, he'd do well to consider Michael Desch, an accomplished scholar who has thought deeply about what's been ailing American foreign policy in recent decades and how to right it. When it comes to the military men Trump has often favored for foreign policy advisers, he could do worse than tap Douglas Macgregor, a retired U.S. Army colonel who has become a staunch critic of American policy since September 11. Another strong option would be Andrew Bacevich, also a retired colonel, as well as an accomplished historian and pundit, whose writing is highly critical of recent U.S. foreign policy, especially in the Greater Middle East.

For those who care about the future of U.S. foreign policy, the decision about who and what comes after Bolton is likely to be among the most momentous of the Trump administration.

Want more essential commentary and analysis like this delivered straight to your inbox? Sign up for The Week's "Today's best articles" newsletter here.