After President Donald Trump’s first 100 days in office, a “Trump doctrine” has yet to emerge fully, but one important lesson is already clear: making radical changes in American foreign policy is very difficult.

Trump’s surprising victory in the 2016 election portended a dramatic break with the traditional approach to American foreign policy. Since World War II, no other presidential candidate from either party had ever challenged the liberal internationalist strategy of the United States so explicitly, or so successfully.

His populist campaign slogan, “America First,” was never a precise guide to his thinking, but the outlines of a doctrine were always visible. In addition to disavowing the wars in Iraq and Afghanistan, forswearing nation-building, and criticizing the uneven costs of alliances and the liberal world order, Trump staked out a nationalist agenda that included protectionist trade policies, stricter immigration policies, and a more hawkish approach to combating the self-proclaimed Islamic State.

But after all the talk on the campaign trail, it’s hard to find many clear signs of Trump’s “America First” strategy or radical shifts in U.S. foreign policy. Even Trump’s own team is having trouble. At a planning session to discuss messaging about Trump’s first 100 days, in fact, communications advisor Mike Dubke told staffers that foreign affairs was going to be a challenge because “[t]here is no Trump doctrine.” At least on paper, he was correct. The list of “America First” successes is short. Trump did sign an executive order officially withdrawing the United States from the Trans Pacific Partnership trade deal. But since that deal was already dead in Congress, the move was mostly symbolic.

Meanwhile, the list of unfulfilled promises remains long. There is no border wall. There is no ban on Muslims entering the country. The Iran deal remains intact. Trump has not yet renegotiated NAFTA, nor has he gotten tough with China on trade. The United States remains embroiled in nation-building efforts in Afghanistan, Trump bombed the Syrian regime, and we continue to reassure treaty allies with reliable security guarantees. In essence, Trump has discovered what all new presidents learn: It’s easy to call for change, but hard to make it. It is much easier to tweak a policy than to overhaul it completely. In fact, on issue after issue, the Trump administration appears to be settling into an approach to foreign policy that exhibits more continuity with past administration than divergence. The reasons for this are important, but also can shed light on how the next few years of the Trump presidency are likely to shake out.

Political Reality

In part, the lack of follow-through is what happens to every president’s campaign rhetoric when it meets political reality. Though “America First” worked well for Trump on the campaign trail, he quickly discovered that his slogans weren’t much of a guide once he was in charge. After calling NATO obsolete, for example, Trump changed his mind after he learned more about it, acknowledging that, “People don’t go around asking about NATO if I’m building a building in Manhattan, right?” Rather than pulling out of the alliance or calling for major changes to the American role in NATO, Trump has limited himself to nagging allies to increase defense spending, just as every president before him has done. Similarly, after promising to rip up NAFTA, a trade deal he repeatedly called a “disaster,” the administration has recalculated after hearing from a chorus of potential opponents to the move. As a result, Trump now plans to seek more modest amendments to the agreement.

In other cases, Trump appears to have changed his mind about the political costs of radical change once in power. When Trump confronted Chinese President Xi Jinping about North Korea, for example, he got a crash course on the issue and changed his mind. “After listening for 10 minutes, I realized it’s not so easy,” Trump admitted. “I felt pretty strongly that [China] had tremendous power” over North Korea, “but it’s not what you would think.” Trump also discovered that a lot of what he thought he knew just wasn’t so, including the fact that, contrary to his own repeated claims, China was no longer engaged in currency manipulation.

Institutional Roadblocks

Trump has also run into the institutional roadblocks that stand ready to frustrate all presidents. As much power as presidents wield in the national security realm, many policies require the help or approval of other branches of government. Trump’s executive order to restrict travel from seven, later six, Muslim-majority nations, for example, has twice been blocked by the federal courts and will have to overcome constitutional challenges before it comes into effect.

Nor has Congress been any more helpful with Trump’s signature issue, the Mexican border wall. Trump issued an executive order calling for the immediate construction of the wall, but the follow through will depend on Trump getting funding from Congress. However, now that Mexico’s leaders have said they won’t pay for it, Congressional Republicans have made it clear that they are not willing to pony up either.

The Rest of the World

Another challenge to Trump’s efforts is that the rest of the world is not making it easy to change gears. Thanks to long-standing expectations of American leadership, the pressure to act in response to events abroad can be overwhelming. The best example of this is the Assad regime’s use of sarin gas against civilians in Idlib. After seeing graphic images of the tragedy, Trump felt compelled to respond with military force. He did so despite having opposed a similar attack in Syria when Obama was in office. The inconsistency between Trump’s “America First” campaign rhetoric, and his behavior as president, reveals how difficult it is to resist the pressure to play global policeman.

In other cases, change is difficult because the facts on the ground simply leave little room for strategic innovation. North Korea’s development of long-range missiles and nuclear weapons continues to provoke U.S. concerns, but despite tough talk the Trump administration has few real options other than to work with China and others in pursuit of a diplomatic solution. Likewise, Trump’s desire to pursue a more aggressive campaign against the Islamic State is stunted by the fact that there is simply no way to speed up the battle short of sending tens of thousands of American troops back into harm’s way. As a result, Trump’s Islamic State strategy looks a lot like an amped-up version of Obama’s strategy.

Where Art Thou, America Firsters?

Another factor in Trump’s gradual bend towards foreign policy convention comes down to personnel. So far, Trump has only managed to confirm 22 of the more than 500 federal appointments that require Senate confirmation, many of them in the national security realm. This makes implementing policy, never mind tectonic shifts in strategic posture, much harder.

The personnel shortage influences even the highest reaches of Trump’s own cabinet. Early on, the prominence of volatile hawks like retired Lt. Gen. Michael Flynn and brash ideologues like Steve Bannon produced an approach that tended to amplify Trump’s policy illiteracy and spurn the experts within the national security bureaucracy. Now, with Flynn ousted and Bannon possibly marginalized, mainstream Republican foreign policy views held by people like Defense Secretary Jim Mattis, National Security Advisor H.R. McMaster, and U.N. Ambassador Nikki Haley have gained greater purchase in the White House’s approach to the world.

The ascendance of more traditional Republican foreign policy officials has coincided with Trump’s decision to give greater leeway to military leaders. President Obama was sometimes criticized for micro-managing military actions in Afghanistan, the fight against the Islamic State, and the drone war. Trump has gone the other way and authorized the military to engage in airstrikes, special operations raids, and troop deployments with wide latitude. This has necessarily meant an approach more in line with traditional U.S. foreign policy and less consistent with “America First” ideas.

A more fundamental challenge underlying the personnel issue is the fact that, for more than 70 years, Washington has been dominated by a particular set of ideas about the need for a grand strategy of deep engagement, an activist foreign policy, and American leadership of the international system. Staffing the executive branch with “America Firsters” is hard to do — mainly because they don’t exist anywhere in the Washington foreign policy community. As a result, when Trump gets advice from mainstream military leaders and other veteran policy advisors about Syria, North Korea, or Russia, their advice comes steeped in the assumptions of liberal internationalism.

Process Trumps Doctrine

But perhaps most detrimental to Trump’s “America First” vision is the fact that the Trump doctrine has taken a backseat to the Trump process.

For starters, Trump does not seem entirely wedded to his own “America First” doctrine. Despite the manifestly ideological nature of the Trump campaign, to most observers it looks like Trump — for good or ill — simply does not yet have well-formed opinions about how to confront the many foreign policy challenges the United States faces. As president, Trump thus appears to be ideologically unmoored, priding himself on “flexibility,” and eager to abandon ideas that helped get him elected if they seem to hamper effective governance. The result has been a series of flip-flops on matters of policy without a hint of hesitation or shame.

The lack of ideological principle translates to a lack of strategic deliberation. Trump’s missile strikes on Syria and his saber rattling on North Korea both smack of a desire to look tough, but neither are part of a serious broader strategy. The Syria strikes will not mitigate the humanitarian suffering there and were not even intended to affect the balance of power in the civil war. And the threats of preventive war on North Korea won’t compel Pyongyang to denuclearize. In the absence of an overarching ideological or strategic approach, short-term tactical considerations tailored to achieve quick but small wins rule the day.

The “America First” program remains at the mercy of Trump’s personality and governing style. On this score, a review of his first 100 days in office makes clear that Trump injects an element of unpredictability to the entire foreign policy enterprise. Trump’s tendency to comment on breaking news and to create foreign policy on the fly via Twitter, often without warning his senior advisors first, not only worries old foreign policy hands but raises the chances that Trump will call an audible rather than stick to the “America First” playbook. Perhaps the only consistent theme in Trump’s approach is the desire to bolster his domestic legitimacy and shore up American prestige abroad. Those motivations, we note, have so far pushed Trump toward greater foreign policy activism, not “America First” isolationism.

What Does the Next Hundred Days Hold?

At just 100 days in it is impossible to know what form a Trump doctrine will finally take. Given how much momentum the status quo has, and how lightly Trump appears to hold his vision of America First, the most likely outcome is something that looks a great deal like the strategy of liberal hegemony pursued by the past two presidencies. Trump will fight terrorism, support America’s global alliance system, and continue to field the world’s largest and most capable military, occasionally using it to intervene abroad out of humanitarian and security concerns.

Nonetheless it is certainly possible that the rest of Trump’s term will look more “America First” than the first 100 days have. Though overhauling NATO or significantly reducing America’s role in the world will be difficult, with time, Trump might overcome some of the institutional roadblocks on immigration reform and economic protectionism.

Domestic political pressures may also encourage Trump to seek a deeper embrace of America First. In the short term, Trump may get away with experiments in foreign policy that depart from his rhetoric. But Trump eventually faces the prospect of a second presidential campaign. And though foreign policy typically plays a muted role in elections, the genius of Trump’s vision of “America First” was the way it connected foreign affairs with domestic outcomes. Trump criticized intervention and nation-building because they hurt working Americans. For Trump, unlike for other presidents, pursuing an interventionist and internationalist foreign policy risks abandoning his political base. Thus, as his term proceeds, Trump may feel the need to take a more visibly nationalist approach to foreign policy to boost his chances for reelection.

Trevor Thrall is senior fellow at the Cato Institute and associate professor at the Schar School of Policy and Government at George Mason University.

John Glaser is Associate Director of Foreign Policy Studies at the Cato Institute.