President Obama’s August 31 decision to seek Congressional support for military action against Syria caught nearly everyone by surprise. Many in the Middle East and elsewhere see it as a sign of White House indecision—or worse, that the president would not mind being able to blame Congress for not taking military action. Recovering presidential credibility will not be easy.

Over the past two years, the president has taken a cautious attitude toward Syria. Having extracted the United States from Iraq and on the verge of a significant reduction in the U.S. military presence in Afghanistan, he shows little desire to engage in yet another conflict in that part of the world.

Syrian President Bashar Assad has waged an abhorrent military campaign, leaving some 100,000 Syrians dead and millions displaced. He has inflicted a horrific humanitarian tragedy on his own people. In an ideal world, the international community would react with more than just revulsion—but it has not and likely will not. Russian support for Assad assures that the UN Security Council will take no serious action.

It is not the duty of the United States to fix every injustice in the world. Mr. Obama seems to believe that U.S. military power could not make a significant difference in Syria, at least not at a price the United States is prepared to pay. Part of the problem is the mix of Syrians in the “rebel” camp: some aspire to a democratic Syria, but Islamist forces—including those close to al-Qaeda elements—have gained in influence. How could the United States strike and help the former but not the latter? The president’s hands-off approach is understandable, and is a policy with which I agree.

The chemical weapons attack by Syrian forces on the suburbs of Damascus on August 21 killed some 1,400 Syrians and introduced a significant new factor, particularly as Mr. Obama in August 2012 had drawn a “red line” against chemical weapons use by the Assad regime.

In the aftermath of the attack, the Obama administration began laying the groundwork for a military strike, apparently seeing military action as necessary to maintain U.S. credibility. The U.S. Navy positioned warships armed with Tomahawk cruise missiles in the eastern Mediterranean within range of Syria, while U.S. officials suggested a one- or two-day campaign based largely on cruise missile strikes.

A number of observers questioned the wisdom of a limited punitive action. Senators McCain and Graham, ever eager to entangle the United States in new military campaigns, escalated their calls for a major effort to oust Assad, though without putting American soldiers on the ground. My Brookings colleague Ken Pollack wrote in Newsweek that the United States should “do nothing or pursue an intervention far more decisive than limited strikes.” It is a thoughtful, well-argued piece, even if one disagrees with the bottom line.

There is a rationale for a more limited action: to show Assad that using chemical weapons has risks and costs, in the form of military strikes by the United States, France and possibly others. The goal is to alter Assad’s calculus. Two weeks ago, all evidence suggests that Assad felt he could use chemical weapons with impunity.  A punitive military strike would demonstrate that such action has costs and might—might—affect his future calculations. That seems a logical and defensible objective, even if the United States is not prepared to engage more broadly in the conflict, though having conducted a punitive strike, Washington would need to exercise care not to get pulled in too far.

The United States and other Western powers built toward this kind of action the week of August 26.  Then came the surprise from London. Prime Minister Cameron, who had urged a military response, asked his Parliament for support—and lost. Some 60 members of his own Conservative Party either did not vote or opposed the government motion, which failed by thirteen votes. As Gideon Rachman wrote in an excellent article in the August 30 Financial Times, No. 10 Downing Street and Conservative Party leaders mismanaged the vote, failing to understand that support in their party for military action was soft.

While the British vote posed a setback for broad international action, U.S. officials indicated that Mr. Obama nevertheless intended to proceed. Paris signaled that it also remained ready to act; President Hollande planned to consult but not ask for approval from his legislative branch. On August 30, Secretary of State Kerry described U.S. evidence regarding the nerve gas attack and the responsibility of Syrian forces in a compelling appearance before the press.

The next day, Mr. Obama caught almost everyone short with his curve ball, saying that he had decided on the use of force but wanted Congress’s support for military action.

There is logic to seeking to have Congress on board. A military strike conducted with Congressional support would send a stronger message of American resolve. But the president should have called on Congress to come back into session the week of August 26 to debate and vote on his request. At the least, having waited until August 31 to seek Congressional support, he should then have asked Congress to return early from its summer recess. Instead, he will seek a vote when Congress comes back on September 9.

The president said the targets could be hit in a week or a month just as well as now. True enough. But what political message did his statement send to our adversaries and friends? It signaled White House hesitation and indecision about the use of force. Some undoubtedly believe the president would welcome a Congressional “no” vote as letting him off the hook in the same way that the Parliament’s vote has taken Britain out of the military game. Damascus applauded his decision as a victory.

Congressional support for military action is far from guaranteed. Many in the Democratic Party have doubts about the wisdom of any military involvement, and the president will need Republican votes. But the White House has awful relations with the Republicans. While the party would almost surely rally to a Republican president’s call for military action, some in the Republican ranks are dubious about a punitive strike. And a number of Republicans will oppose any resolution simply to spite Mr. Obama, no matter how much damage is done to U.S. international credibility.

By waiting until Congress returns on September 9, the president has undercut the political momentum for action his administration had built during the week of August 26 and gives opponents time to mobilize their numbers. He will need to do some hands-on lobbying, but he is scheduled to spend most of the week in Sweden and St Petersburg, Russia.

Some administration officials suggest that, even if Congress votes down a resolution on military action, the president could nevertheless order a strike. He may have the authority as commander-in-chief—that’s a question for constitutional scholars to debate. But could he give such an order politically following a defeat in Congress?

The president has set a course while leaving his ability to pursue it in the hands of others, including those not well disposed toward him. I hope the White House knows what it is doing.  Right now, it is very hard to tell.