Several hours earlier, at an NSC meeting that afternoon, the president had approved military targets. We were very close to launching. Our primary impediment was the UN, which needed time to move its personnel out of harm’s way. We had lined up international partners to join our military operation, notably France and the U.K. But Prime Minister David Cameron decided to seek parliamentary approval for this action, and, shockingly, he lost the vote. This was a major setback, but France remained gung ho.

When White House senior advisers gathered that Friday evening in the Oval Office, Obama began with his description of the challenge he aimed to address. We did not have a clearly valid international legal basis for our planned action, he said, but we could argue that the use of banned chemical weapons made our actions legitimate, if not technically legal. Domestically, we could invoke the president’s constitutional authority to use force under Article II, but that would trigger a 60-day clock under the War Powers Act—meaning that if our actions lasted longer than 60 days, he would need to obtain congressional approval to continue military action. Therefore, before we used any significant force in Syria to address its chemical-weapons use, the president thought it best to invest members of Congress in the decision, and through them the American people.

As usual, Obama was thinking several plays down the field—to the potential need for military action against Iran, should diplomacy fail to force that country to give up its still nascent nuclear-weapons program. Once the precedent was established that Congress should act to authorize military action in Syria, we could insist on the same kind of vote should we need to confront Iran—a much higher-risk proposition that he would want Congress to own with us.

I admired the president’s logic, but disagreed with his assumptions. As Obama polled the aides assembled in the Oval, all agreed with him. He called on me last, as he often did in my role as national security adviser.

The lone dissenter, I argued for proceeding with military action, as planned. We had clearly signaled—most recently that morning in a strong speech by Secretary of State John Kerry—that we intended to hold Syria accountable through the use of force. Our military assets were in place. The UN had been warned. Our allies were waiting. As then–Vice President Joe Biden liked to say, “Big countries don’t bluff.” Finally, I invoked the painful history of Rwanda and predicted we could long be blamed for inaction.

Above all, I argued to the president, “Congress won’t grant you the authority.” That was my strong gut instinct. Bitter experience had shown us that Republicans in Congress were so hostile to Obama that they would deny him anything of consequence he requested, even if they believed that what he requested was right. I anticipated that congressional Democrats would splinter, as many did not want to vote for what they feared might become another war of choice in the Middle East. The president listened closely to us all and acknowledged my concerns. He concluded his argument with characteristic aplomb, predicting that we would get the votes in Congress. I was neither a political strategist nor the legislative-affairs director, nor had I been elected president twice. So I rested my case.