The resignation of Defense Secretary James N. Mattis was only a matter of time – President Trump referred to him as ‘sort of a Democrat’ in October – but it could hardly have come at a more turbulent moment. Earlier on Thursday the Dow was once again crashing. Washington was headed toward a shutdown over the $5 billion that Trump has demanded for a border wall. Then came the resignation letter of Mattis, widely seen as the last ‘adult in the room,’ as the phrase had it, in the Trump administration. Now that Trump has disemboweled his national security team, he, and he alone, will bear responsibility for the consequences of his actions.

Mattis, who rebuffed White House pleas to support Trump’s Syrian withdrawal decision, made his disdain for Trump’s approach to foreign policy clear, stressing the need to work with allies to preserve American national security. Trump, he said, deserved a Defense Secretary ‘whose views are better aligned with yours…’ Trump stated in a tweet that Mattis served ‘with distinction,’ but it can’t be long before he issues a tweet referring to Mattis as ‘dopey,’ ‘dumb as a brick,’ ‘a moron,’ or some other choice epithet about the four-star general he previously lauded.

The reason that Mattis’s move will hurt Trump more than he has probably reckoned is that it further erodes his relationship with Senate Republicans who ultimately control his fate. Until now, they have been largely quiescent in the face of Trump’s serial provocations to Republican foreign policy orthodoxy. But his vow to remove all US troops from Syria and apparent plans to withdraw about half of troops stationed in Afghanistan, which flies in the face of the hawkish anti-terrorist policies that the GOP espoused since 9/11, has set the stage for a civil war over America’s purpose abroad inside the GOP. Appearing on CNN, Trump adviser Stephen Miller said that Trump’s mission was to remedy ‘our foreign policy’ following ‘one foreign policy blunder after another’ in Iraq, Afghanistan and Libya. ‘When did the American people sign up to be in every war, in every place, on every side, of every conflict all over planet earth?’

But such rhetoric isn’t sitting well with other Republicans. Sen. Lindsey Graham, an inveterate hawk, announced that pulling out of Afghanistan would lead inexorably to ‘a second 9/11.’ Sen. Marco Rubio declared that Mattis’s resignation ‘makes it abundantly clear that we are headed towards a series of grave policy errors which will endanger our nation, damage our alliances & empower our adversaries.’ Russian president Vladimir Putin’s comment, ‘Donald’s right, and I agree with him’ only poured more salt into Republican wounds.

Indeed, Trump’s rush to exit Syria and Afghanistan is already raising questions about his motives, with some suggesting that he’s doing it to appease Putin, while others argue that he wants to distract attention from his domestic woes. It’s also possible that he’s simply embracing his inner isolationist. Like any number of foreign policy realists, he believes that America has been overextended abroad and must retrench.

Trump appears to be intent on becoming a foreign policy president. Like many of his predecessors, he is hemmed in domestically but has running room in foreign affairs. If he can pullout of Syria and Afghanistan, his next target will be saying hasta la vista to NATO. Taiwan, South Korea, and Japan must also be casting a nervous eye at the prospect of a Trump unbound. He is reverting to the doctrines that originally helped him win the Republican primary and that represent a reversion to pre-World War II Republican doctrines – high tariffs, restrictive immigration measures and an isolationist foreign policy. Trump’s views have been hiding in plain sight for years. Now he’s acting on them.