Barack Obama’s presidency has not been about restraining the powers of the presidency. On major issues both domestic and international — immigration, environmental regulation, the war in Libya, and more — Obama has shown no hesitation to act unilaterally in areas that properly lie within the purview of Congress. But now, the president says that even though he has decided the U.S. should attack the Syrian regime over its use of chemical weapons, he will ask Congress to give him permission to do so.

It’s not entirely clear why Obama has decided to exercise restraint now when he has not done so in the past. Has he experienced a sudden conversion in which he gained new respect for the Constitution’s limits on executive authority? Does he really want to do nothing, and secretly hopes Congress will reject his proposal? Or has he made an essentially political decision to make sure Congress shares the blame for any calamity that might result from his lack of a clear Syrian policy?

Whatever the reason, one thing is clear: Obama has set up a potentially critical confrontation between the executive and the legislative branches. It won’t be about the substance of what he proposes to do, that is, whether is it a good idea to attack Bashar al-Assad’s forces or not. Instead, it will be about whether a president is bound to follow the will of lawmakers who have the ultimate constitutional authority over whether the nation goes to war.

The simple question: If Congress rejects Obama’s proposal, will he abide by its decision, or will he use his powers as commander-in-chief to attack Syria anyway?

If Congress authorizes Obama to act, there’s no problem, at least constitutionally. Obama can carry out the attack, or choose not to carry out the attack, depending on his best judgment. But if Congress refuses to give its authorization, Obama faces a stark choice. He could abide by Congress’ decision, and not attack; again, no constitutional problem. Or Obama could argue that as president, in his role as commander-in-chief, he has the authority to carry out the attack on his own, and launch the cruise missiles.

What would happen then? Would Congress protect its own prerogatives and take some action, perhaps using its power of the purse, to stop the president from making war? Or would Congress back down? Either way, one branch of government could come out looking much weakened. As one “senior administration official” told the Wall Street Journal: “You have to win the vote. You have to win. If Congress doesn’t let him act, the consequences for him and for the country’s standing in the world are enormous.”

But Obama has not promised to abide by Congress’ decision. In his Rose Garden statement Saturday, he said he has already decided the U.S. should attack Syria. He said he believes he has the authority to carry out the attack without authorization from Congress. But he said he had decided to seek authorization anyway, because “all of us should be accountable as we move forward, and that can only be accomplished with a vote.”

Note that the president said Congress’ vote was necessary for “accountability,” not that it would decide whether the U.S. attacks Syria or not.

Late Saturday, Fox News, citing a senior State Department official, reported that “the president’s goal to take military action will indeed be carried out, regardless of whether Congress votes to approve the use of force.” Other senior officials told Fox that Obama “is merely leaving the door open” to an unauthorized attack and will “wait to see what Congress does” before deciding whether to attack.

If Obama decides to go ahead in the face of a congressional refusal to authorize force, what will Congress do? Nobody knows. But it will likely lead to an ugly and protracted fight. And it will certainly lead to talk, and perhaps more than just talk, of impeachment.

When Parliament rejected his Syria plan, British Prime Minister David Cameron said, “It’s clear to me that the British Parliament and the British people do not wish to see military action. I get that, and I will act accordingly.” Would President Obama say something similar if lawmakers reject his proposal? It’s hard to imagine that the man who has ignored Congress so often in the past would back down now. Unless that is what he wanted to do all along.