When Congress returns from recess the week of September 8, the US military will have been bombing Islamic State fighters in Iraq for a month. Officials say the bombing could continue for months more, and they’ve also threatened to bomb IS fighters in Syria.

The Constitution and the 1973 War Powers Resolution require congressional authorization to use military force unless there is an attack or imminent threat of attack on the United States. Congress has not authorized force in Iraq or Syria, and whatever one thinks of President Obama’s initial justifications, there is no such thing as an “emergency” of infinite duration.

The constitutional and legal limits on the president’s warmaking powers crucially shape the ability of the public, acting through Congress, to determine when, how and for how long the country goes to war. If a precedent is set now that expands presidential power, the public will pay for it in the future through more war and fewer opportunities to prevent or limit it. Thus we all have a stake in the fight over congressional war powers, regardless of whether you support, oppose or are not sure about Obama’s actions against IS.

The president is not relying for legal justification on the 2002 Iraq War authorization, nor is he relying on the 2001 authorization passed after the 9/11 attacks; he is instead relying on his claimed “inherent” power as commander in chief. That claim was based on the idea that IS threatened Americans before the president began bombing. It was a murky claim then, and it grows murkier with each passing day.

No one disputes that if, say, enemy warplanes are headed into US airspace with apparent intent to strike and refuse warnings to turn away, the president can order them shot down without consulting Congress. But the US personnel in Iraq most clearly threatened by IS were those Obama himself had placed there and declined to evacuate. If IS is now an imminent threat—not merely to “US interests” but to America itself—by virtue of the fact that the United States has been bombing it, then Obama is opening a back door to escape constitutional limits. If bombing proceeds indefinitely on this basis, it would set a dangerous precedent for prolonged military action without congressional approval.

If we don’t want the constitutional and legal limits on presidential warmaking to be eviscerated, we must act. Those limits do not enforce themselves, and in the absence of congressional action, no court is likely to enforce them. If Congress fails to act, courts would likely see that as vindication of the president’s claims, as they have in the past. If we want Congress to act, then the public needs to say so.

Recent polls suggest that about 60 percent of the public currently supports Obama’s airstrikes against IS fighters in Iraq and would also support strikes against IS in Syria. This should not surprise us: the story on TV, where most Americans get their news, has been that Obama and Republicans are on the same side, supporting “targeted” airstrikes against “Islamic terrorists” who “threaten America.”

In the near future, public sentiment on this issue is likely to resemble public opinion on the drone-strike policy in Yemen and Pakistan, which Americans have generally supported unless the strikes kill civilians or aren’t really “targeted” on “terrorists” who “threaten America.” Raising these same questions will be key to challenging US airstrikes in Iraq or Syria. But if the politics on drone strikes are any guide, this may be a long struggle, since IS has now demonstrated the means and motive to kill Americans, and arguably represents a much greater threat to Iraqi civilians than limited US airstrikes. In this context, a frontal assault on Obama’s policy—trying to block any US bombing of IS—is not likely to work.

If we don’t have the votes now to force an end to the bombing, and if it is unacceptable to do nothing, what remains is pressing Congress to enact limits. The most important of those limits is time: Congress can “sunset” any authorization of force by stipulating an expiration date. That would act as a brake on endless war and mission creep by putting the onus on supporters of the war to justify its continuation. There’s an important precedent for such a provision: in May, Representative Adam Schiff offered an amendment to make the 2001 authorization expire in a year, so that Congress would have to consider a new authorization of force for the campaign formerly known as the “global war on terror.”

This time limit is important because it helps enforce all other limits. Congress should also contain the war geographically by restricting it to Iraq, or to Iraq and the Iraq-Syria border. Other limits include restricting targets to IS fighters, so the war doesn’t morph into intervention in Syria’s civil war, and a requirement for regular public reporting on civilian casualties, so this issue doesn’t become an unaccountable fog as it has in Pakistan and Yemen.

Nothing in Washington, including respect for the Constitution, happens by itself. Every reform requires agitation.