For Washington’s national security community and overseas allies, the departure of US Defense Secretary Jim Mattis is a nasty surprise. President Donald Trump started 2018 with a triumvirate of respected current and former generals seen as central to restraining his wilder foreign policy instincts. Now that constraint will soon be gone, leaving US international relations hugely less predictable.

Here are four of the most immediate implications of the Mattis departure:

One: Trump is now making his own foreign policy.

It began earlier this year with the ousters of national security adviser Lieutenant General H.R. McMaster and Secretary of State Rex Tillerson and continued this month with the announced departures of White House Chief of Staff John Kelly and now Mattis. All four individuals were seen as moderating influences on Trump on issues like potential strikes on North Korea or US military support for NATO and Asian allies. By the end of February, all will have departed - with replacements such as conservative national security adviser John Bolton seen as much more willing to follow Trump’s direction.

This has implications on fronts ranging from trade to nuclear weapons policy. After the G20 meeting in Buenos Aires ended on Dec. 1, Trump tweeted his intent to meet with Russian and Chinese counterparts Vladimir Putin and Xi Jinping in the new year to address global tensions and the arms trade. The US president is now likely to be entering those meetings - if they ever take place - feeling less restricted in his options. The same goes for an anticipated second summit with North Korean leader Kim Jong Un. A more unfettered Trump may well be more isolationist, but also potentially more prone to dramatic, impulsive action.

Two: In the Middle East, America will let others call the shots.

Mattis’ resignation letter indicates that Trump’s unexpected announcement of an immediate US troop withdrawal from Syria, coupled with a pullback of troops from Afghanistan, was the last straw for the defense secretary. Throughout the Trump presidency, the Pentagon has advocated ferociously for more resources for both conflicts despite the president’s long-running antipathy towards long-term military interventions in the region.

If Trump goes ahead with the withdrawal, there will be dramatic implications on the ground. In Syria, the move will likely embolden both Turkey and the Russian-backed forces of President Bashar Al-Assad fighting against America’s former Syrian Kurdish allies. European states - most likely led by Syria’s former colonial power France - will have to decide fast if they wish to fill the gap left by the US departure.

Washington appears to be signaling that it will simply be less involved, essentially leaving the field to the growing confrontation between the regional powers. The White House will likely want to keep up the pressure on Iran’s nuclear program using sanctions and other means, but will probably not intervene otherwise.

Three: Asian and European allies will be nervous.

Throughout Trump’s two years in office, much of Mattis’ role has been to travel the globe placating America’s allies and reassuring them of Washington’s long-term support. His departure will leave them wondering what those guarantees were worth - and watching the White House closely for signs of how policy will now change.

The biggest question will be whether Trump attempts to tamper with US commitments in Europe and Asia, where Washington has continued to step up military activity in the face of increasingly assertive Russian and Chinese action. Trump has been repeatedly critical of America’s allies, saying they have done too little to secure their own defense and have become too reliant on Washington’s spending.

After his meeting with North Korean leader Kim Jong Un in June, Trump shocked many in his own administration by pledging to cease joint exercises with South Korea in the hope of reducing tensions. The real nightmare for many in the Pentagon, NATO and beyond is that he may now do the same with military activities in Europe, Asia, or both, possibly emboldening America’s most powerful potential foes and driving up the chances of an inadvertent conflict.

Four: America may become both more isolationist and volatile.

Much will depend on who Mattis’ replacement turns out to be - a choice that will be shaped both by who Trump will tolerate and who might be willing to take the job. Overall, however, experience suggests that any appointee will have to embrace a Trumpian worldview that is more isolationist and sometimes more reactionary than much of the US national security establishment would wish.

What that means is remarkably hard to model - not least because Trump himself has been so inconsistent. He has talked repeatedly about building a strong US military - but last month suggested he might cut it as part of the deal to slow the arms race. He has been openly cautious of military action - but stepped up US airstrikes in Afghanistan and elsewhere. In confrontations such as those with Russia and China in Eastern Europe and the South China Sea, he could easily take either a much more aggressive or conciliatory approach.

We’ve seen this dynamic with North Korea, where Trump was initially seen as keener than the Pentagon to consider military action, only to then offer greater concessions than the national security establishment considered wise. That dynamic is now in play on a global scale, and it could go either way. Also complicating matters is Trump’s political position at home, where he faces a deadlocked Congress, the endgame of Special Counsel Robert Mueller’s investigation into alleged collusion with Russia and the start of the 2020 presidential campaign.

Bottom line: 2019 was already looking volatile. The departure of Mattis makes it dramatically more so.

Reuters

— Peter Apps is Reuters global affairs columnist.