DURING A visit to Washington in late August, Gen. Wissam al-Hassan, the intelligence chief of Lebanon’s internal security forces, offered a grim assessment of the civil war raging in neighboring Syria and its likely impact on the region. Dictator Bashar al-Assad, he told us, still had a chance to outlast the rebellion against him, though “it will take a couple of years and more than 100,000 killed.” For the Assad regime, he added, “one of the solutions of the Syrian conflict is to move it outside Syria. He survives by making it a regional conflict.”

A little more than seven weeks later, Mr. Hassan was dead, killed in an Oct. 19 car bombing in Beirut that has taken Lebanon to the brink of its own sectarian war. Most Lebanese not allied with the Hezbollah movement agree with former prime minister Saad Hariri that “it is clear as day” who sponsored the assassination. In short, Mr. Assad is attempting to implement the very strategy that Mr. Hassan spoke of.

The intelligence chief was a key member of the pro-Western group that governed Lebanon for several years after the 2005 “Cedar Revolution” forced Syria to end 30 years of military occupation — and he had been fighting to prevent Mr. Assad from meddling in his country. In August, he exposed a plot by a former Lebanese cabinet minister with close ties to Mr. Assad who had conspired to smuggle explosives into the country for a series of bombings. He was pressing Lebanon’s weak prime minister, Najib Mikati, to order the disarmament of a pro-Syrian militia that had provoked clashes in northern Lebanon.

But Mr. Mikati is constrained by Hezbollah, a Syrian client that is the strongest force in the current government. “Mikati won’t move” against Syria’s provocations, Mr. Hassan told us, “unless Assad is dead or outside the country.”

Mr. Hassan proved all too prescient. Mr. Mikati has done little to respond to the bombing — the worst such attack in Lebanon in four years — other than to deploy the army to quell incipient sectarian clashes. He has refused to resign, a step that could open the way to the formation of a government that does not include Hezbollah. In this, remarkably, he had the support of the Obama administration, whose first response to the attack was to dispatch the U.S. ambassador in Lebanon to join her Russian and Chinese colleagues in meeting the president to appeal for “stability” in the country.

The State Department subsequently softened that stance, saying that it would support a “process leading to a new government.” But in Lebanon as well as Syria, the Obama administration is pursuing the shortsighted policy of seeking to restrain anti-Assad forces. That strategy has had no effect in either country other than to empower U.S. enemies and jihadist groups, whose foreign sponsors are showering them with weapons and cash.

Mr. Hassan warned us that the prolongation of the fighting in Syria would lead “to sectarian war and a destroyed civil society.” He added: “The [Syrian] Army will disintegrate, and after its collapse there will be chaos.” By refusing to arm or protect secular and liberal forces, the Obama administration is helping to ensure that outcome.