For almost two years now, President Trump has seemed clear-eyed about the threat posed by those who proudly call themselves jihadis.
He appointed a top-notch national security team determined to crush the non-state actors who use terrorism to establish Islamic supremacy, and to at least contain the Islamic Republic of Iran. And then, last week, he abruptly reversed course.
Rejecting the advice Secretary of Defense James Mattis, National Security Adviser John Bolton and Secretary of State Mike Pompeo, Mr. Trump said he was withdrawing all U.S. troops from Syria, and about half the 14,000 troops still in Afghanistan.
The strategic errors made by President Obama — who was never clear-eyed about the jihadi threat — spring to mind. In 2011, ignoring his national security advisers, he withdrew all U.S. troops from Iraq. That led to the rise of the Islamic State — by no means a "JV team" — and opened Iraq's doors to Iran's rulers.
Mr. Obama went on to enrich and empower Tehran in exchange for a deal based more on trust than verification, a deal aimed to slow but not stop its acquisition of a nuclear weapons capability.
Also beginning in 2011, Mr. Obama decided to do nothing to assist those in Syria protesting the oppressive dictatorship of Bashar al-Assad, a client of Iranian Supreme Leader Ali Khamenei. Among the consequences of Mr. Obama's inaction over the years since: half a million dead Syrian men, women and children, and a flood of refugees into Europe where their impact has been destabilizing, to put it mildly.
In Afghanistan, too, Mr. Obama's policies never achieved coherence or consistency. Perhaps most egregious, in late 2009 he announced a 30,000-troop surge, quickly adding that "after 18 months, our troops will begin to come home." In other words, he told the Taliban and al Qaeda that if they would just hunker down for a while, they'd be fine. So they did, and so they were.
For almost two years, President Trump has taken a different approach. A small but highly effective force in eastern Syria, about 2,000 troops, mostly special operators supported by Air Force and Navy combat planes, working with local allies, has evicted Islamic State fighters from most of the territories they had conquered.
That counts as significant progress. But to say, as Mr. Trump did last week, that the Islamic State has been defeated is premature. An estimated 30,000 fighters remain in Syria and Iraq. We must now expect them to revive and rebuild under the leadership of Abu Bakr al Baghdadi whom we've not yet tracked down and eliminated.
America's military presence also has succeeded in preventing Iran's rulers from establishing a land bridge through Syria into Lebanon — now effectively ruled by Hezbollah, Tehran's proxy — and on to the Mediterranean.
Useful too: About 90 percent of Syria's oil lies under territory controlled by the United States. Those resources will soon replenish Mr. Assad's coffers, reducing the amount Ayatollah Khamenei spends — an estimated $16 billion annually — to prop up the mass-murdering dictator.
That will leave more money for terrorists and missiles that can deliver nuclear warheads. The financial pressure Mr. Trump has been applying to coerce concessions from Tehran will be weakened.
Other beneficiaries of the withdrawal include Vladimir Putin who, on President Obama's watch, was able to re-establish a Russian foothold in the Middle East for the first time since the Cold War, and Turkish President Recep Tayyip Erdogan, an authoritarian and supporter of the Muslim Brotherhood.
I'm afraid that's not all. Leaving Syria too soon means abandoning the moderate Arab, Syrian Christian and Kurdish forces who have fought with us against the Islamic State. It is likely they will surrender to, or be slaughtered by, Syrian and Turkish forces. Perhaps some combination of the two.
Jordan and Iraq — nations in which we've made significant investments — will face additional peril. Israelis will be under more pressure, too.
In a letter of resignation precipitated by Mr. Trump's announcements, Gen. Mattis made clear that he could not, in good conscience, implement a self-defeating policy and abandon allies who have fought with us, and put their trust in us.
For almost two years, President Trump seemed to understand what Mr. Obama did not: That those who proudly call themselves jihadis cannot be appeased; that to defeat them will require a theory of victory, combined with a strategy, ample resources, patience, and a will of iron.
The war now underway began 40 years ago next month when an unexpected revolution gave birth to the Islamic Republic of Iran, the first modern nation-state committed to a conflict whose long-term goal has been stated unequivocally and repeatedly: "Death to America!" The war broadened in 2001, when al Qaeda slaughtered Americans on American soil.
That attack brought U.S. troops into Afghanistan to topple the Taliban, al Qaeda's host. The Taliban fought on, undaunted. It now knows it will prevail. Ayman al-Zawahiri, the al Qaeda leader who succeeded Osama bin Laden, and whom we've failed to track down and eliminate, can be confident that not for the last time is he seeing infidels in retreat.
Mr. Trump is not wrong to want an end to this long war. Nor was President Obama. But both failed to take to heart George Orwell's famous insight: "The quickest way of ending a war is to lose it." Perhaps, over the days ahead, Mr. Trump will ask himself whether that's really his way.