David Ignatius

Even for a president who advertised his coldblooded pragmatism, the moral dimensions of leadership find a way of penetrating the Oval Office. In the case of President Trump, the emotional distance seems to have been shattered by simple, indelible images of suffering children in Idlib, Syria.“When you kill innocent children, innocent babies – babies! – little babies ... that crosses many, many lines. Beyond a red line, many, many lines,” Trump said Wednesday, his voice high and stretched, after pictures surfaced of lifeless infants choked to death by poison gas.

The recognition: The Syria slaughter “is now my responsibility.” And the admission: “I do change.”

With that conviction, Trump took military action Thursday night, ordering retaliatory missile attacks on a Syrian air base. American interventionism is our best and worst national trait. Historically, until 1941, the United States was a reluctant warrior, fearful of foreign entanglement. Thursday marked the 100th anniversary of America’s entry into World War I, a conflict that still drips with senseless, dutiful killing. The young men of Europe had been slaughtering each other since 1914, but on the other side of the Atlantic it was “America First” until Congress backed Woodrow Wilson and declared war on April 6, 1917.

Trump’s wariness on Syria had been like President Barack Obama’s: He said repeatedly, over the past six years and during the campaign, that he opposed more headlong U.S. military actions in quests that might be morally urgent but strategically fuzzy. Republican hawks such as Sens. John McCain (Ariz.) and Lindsey O. Graham (S.C.) had blasted Obama’s reluctance to intervene, but not Trump. Back in 2013, he’d argued against calls to bomb Syria in retaliation for President Bashar Assad’s use of chemical weapons.

Given that Trump’s view of Syria was so similar to Obama’s, his attempt to blame the latest chemical attack there on his predecessor’s alleged weakness was especially dubious. It displayed his embattled, defensive self-image: He is a victim of someone else’s bad decisions. A similarly immature blame-shifting troubled many military leaders after Navy SEAL William “Ryan” Owens died in a Special Operations forces raid in Yemen. “This was something ... they wanted to do – the generals, who are very respected. ... And they lost Ryan,” Trump said.

Why did Assad use nerve gas in Idlib? It’s impossible to know. Maybe it was a signal to an increasingly aggressive Israel that he still had chemical weapons, or maybe it was a warning to Russia that he wasn’t a pawn to be traded in a grand bargain with Trump. But most likely, it was a reaction to the free hand he was seemingly given when Secretary of State Rex Tillerson said a few days earlier during a visit to Turkey that Assad’s future “will be decided by the Syrian people” – meaning that the United States no longer demanded his departure.

Trump has now taken a decisive step that Obama resisted, but he still faces a dilemma of how to bring political change to a Syria shattered by six years of civil war. The irony is that Trump faces the same bad military options for pressing the attack in western Syria beyond this initial strike that Obama did. U.S. military commanders have focused on the battle against the Islamic State in eastern Syria. The Pentagon has a plan for a relatively rapid conquest of Raqqa, the de facto capital of the caliphate of Daesh (ISIS), with a force led by Syrian Kurdish fighters. U.S. troops will augment this assault with heavy artillery, Apache helicopter gunships and forward-deployed advisers. It’s a pragmatic plan for ending the Daesh terrorist threat quickly, even at the risk of offending Turkey and leaving Assad and the political muddle in Damascus. This plan had all the pieces except a final White House stamp of approval.

Then came those pictures of the Syrian children. With Thursday night’s action, Trump reached one of those unforeseen tipping points on which decisions of war and peace so often rest: the sinking of the Lusitania in 1915, the “Zimmermann telegram” of 1917, Pearl Harbor in 1941, the Gulf of Tonkin attack in 1964, the Iraqi WMD delusion in 2003. What all these triggers for war have in common is that people didn’t see them coming.

The World War I centennial is especially haunting as we think about the choices Trump still faces in Syria. A century later, that conflict is still unfathomable, more like a mystery than a settled narrative. Historians who gathered at the National World War I Museum and Memorial in Kansas City, Mo., debated Thursday why it began and why the treaty that ended the conflict proved so unstable.

Trump might study the example of Harry S. Truman, another president who came to office radically unprepared for the global responsibilities he faced. World War I had made Truman. He commanded an artillery battery in the Argonne Forest. Like so many people caught up in war, he didn’t know what he could do until he was tested. Trump now better appreciates the truth of Truman’s famous line: “The buck stops here.”