President Trump’s embrace of isolationism has been a hallmark of his presidency.

It is now at the center of a foreign policy that will remove troops from Syria and cut the U.S. presence in Afghanistan in half.

The president’s “America first” instincts and his willingness to make public his differences with military commanders differentiate him from recent presidents and from many members of his own party.

{mosads}During his visit with American troops stationed in Iraq on Wednesday, he emphasized his distrust of his own generals — who he characterized as repeatedly asking for more time to defeat the Islamic State in Iraq and Syria (ISIS).

It was an unusual message for a commander in chief to give during an inaugural visit to troops in a combat zone after nearly two years in office.

“They said again, recently, ‘Can we have more time?’ ” Trump said of his generals.

“I said, ‘Nope. You can’t have any more time. You’ve had enough time. We’ve knocked them out,’ ” Trump told the soldiers in Iraq, according to pool reports. 

The choice of words was particularly notable given two resignations in the last week that have rocked the Pentagon: Defense Secretary James Mattis and the administration’s special envoy to the anti-ISIS coalition, Brett McGurk.

Mattis resigned in a letter that laid bare his differences with Trump over foreign policy, and that led to sighs of worry from Republicans on Capitol Hill.

McGurk’s departure came as a direct response to Trump’s decision to remove all troops from Syria, which the president justified in a Dec. 19 tweet that said ISIS had been defeated in the country.

“We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency,” he wrote in an assessment that is not shared by Mattis, McGurk or allies like Sen. Lindsey Graham (R-S.C.).

Trump went on to complain in his remarks in Iraq that other nations should be sharing the burden of U.S. military adventures, a theme that he had also sounded when speaking with reporters in the Oval Office on Christmas Day. 

In the Oval Office, he noted, “Right now, we are the policeman of the world and we’re paying for it. And we can be the policeman of the world, but other countries have to help us.”

Trump’s distrust of multilateralism is long-standing. It permeates his views on trade and environmental policy as well as military matters.

But it is particularly striking on matters of armed intervention. In one GOP presidential debate early in his 2016 run, Trump called the Iraq War “a big fat mistake” and accused the administration of then-President George W. Bush of having “lied” about Iraqi weapons of mass destruction.

Last August, while announcing — with obvious reluctance — that he would send another 4,000 U.S. troops to Afghanistan, Trump took pains to point out that the U.S. “is not nation-building again. We are killing terrorists.”

Trump loyalists point to the fact that he was elected in part as a disruptive force. His isolationist instincts were no secret; they were encapsulated in his “America First” slogan. Even as the battles over his foreign policies play out, the government is partially shut down over Trump’s demands that Congress fund a wall on the Mexican border.

The president’s allies say his instincts are broadly in line with an American public that has grown weary of the bloody conflicts that have consumed much of the past two decades. The U.S. invasion of Afghanistan began 17 years ago.

Yet Trump’s moves have alarmed plenty of Republicans, as well as Democrats, who fear that he could create new dangers.

Some fear an Islamic State resurgence once the U.S. leaves Syria, but others point to more nebulous risks. An abdication of the American willingness to be the “policeman of the world” creates a vacuum that global rivals such as China and Russia would be all too eager to fill, they say.

Mattis made a version of this argument in his resignation letter.

“While the U.S. remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies,” Mattis wrote.

The Defense secretary added: “It is clear that China and Russia … want to shape a world consistent with their authoritarian model … to promote their own interests at the expense of their neighbors, America and our allies. That is why we must use all the tools of American power to provide for the common defense.”

Mattis’s resignation and the media coverage that focused on his differences with Trump appears to have sparked further fury on the president’s part. 

Although Mattis originally intended to stay in his post until the end of February, Trump announced that he would in fact replace him at the end of the year with an acting Defense secretary, Patrick Shanahan.

Trump also complained on Twitter that Mattis had failed to see any problems with, as the president characterized it, the U.S. “substantially subsidizing the Militaries of many VERY rich countries all over the world, while at the same time these countries take total advantage of the U.S., and our TAXPAYERS, on Trade.”

Many Republicans are disconcerted by the president’s withdrawal from Syria, arguing that it could leave the door open for an ISIS resurgence just when it appeared that the radical organization was all but vanquished.

Graham called that decision a “disaster” and a “stain on the honor of the United States.” Sen. Marco Rubio (R-Fla.) called it “a major blunder.”

But Trump is not for turning back. 

“We are spread out all over the world. We are in countries most people haven’t even heard about,” he told reporters who traveled with him to Iraq. “Frankly, it’s ridiculous.”

The Memo is a reported column by Niall Stanage, primarily focused on Donald Trump’s presidency.