Congress has the power to expand or constrain the president's war-making abilities. But what if it declines to exercise it?

It's becoming ever more clear that lawmakers lack the appetite to take responsibility for President Obama's war against ISIS. The White House, after a long delay, sent Congress a proposed authorization for the use of military force in February. (The AUMF has become the modern-day equivalent of a declaration of war.) Never mind that the U.S. military had already been bombing ISIS targets in Iraq and Syria for half a year, nor that those airstrikes have continued throughout the two months that Congress has spent reviewing the three-page proposal.

In the last week, the top two Republican leaders in the House have confirmed that Obama's war proposal is going nowhere, and lawmakers are in no hurry to pass an alternative. Kevin McCarthy, the majority leader, told reporters the administration's draft simply could not garner the 218 votes it needed to pass the House. In effect, the president had invited Congress both to approve and to limit his authority to take on ISIS. The proposal's prohibition of the use of "enduring offensive ground combat operations" was intended to draw support from war-weary Democrats, but it ran into opposition from Republican leaders who didn't want to constrain the military. And with liberals complaining that even that language was too broad, it seems nearly impossible that Congress will achieve a consensus on exactly what it wants to allow Obama to do.

The whole exercise has bordered on the absurd. A quick recap: The administration has argued all along that it doesn't actually need new authorization for the war, because the 2001 and 2003 resolutions that Congress passed—and never repealed—allow for military action against ISIS as a terrorist group that branched off from Al Qaeda in Iraq. Speaker John Boehner demanded for months that Obama submit a formal proposal, but when the White House finally did, he left it for dead.

Aides to the speaker told me on Wednesday that GOP leaders are "still interested in passing an AUMF, but we want a real, robust AUMF that reflects a real, over-arching strategy to accomplish what the president says is the goal: destroying ISIS." Obama's proposal, they said, "actually provides him with less authority" than the existing war resolutions Congress passed in the wake of Sept. 11, 2001. That may have been by design. As Benjamin Wittes of the Brookings Institution writes on the Lawfare blog, "Congressional failure to act arguably constitutes acquiescence to [Obama's] broad claim of authority under the 2001 AUMF, since few of the members of Congress who are refusing to pass a new authorization are also claiming that the president lacks legal authority to take action."

Obama, in other words, put himself in a position in which congressional action would strengthen his hand and congressional inaction—always the likeliest outcome these days—would also strengthen his hand, or at least not weaken it.

Wittes might be giving the White House a little more credit than it deserves; it's not clear that this was a deliberate strategy. But after more than six years in office, Obama has a much better sense of what Congress can and cannot accomplish. That is especially true after his experience in 2013, when his push for congressional authorization to use force against the Assad regime in Syria similarly went nowhere.

Yet Congress's whiff on an ISIS resolution is also instructive as lawmakers prepare to debate the Obama administration's potential nuclear agreement with Iran. The legislature scored a rare victory on Wednesday by forcing the White House to accept a role for Congress in reviewing the deal before it takes effect. That concession, however, doesn't make Capitol Hill an equal partner, as the only way a deal could be scuttled is for opponents to garner a two-thirds majority reject it. And as we've learned in recent years, just because Congress demands a voice in foreign affairs doesn't mean it can find a way to use it.