Congress needs to take a page from Senator Kaine’s playbook and reform the War Powers Resolution of 1973.

This weekend, Democratic vice presidential nominee Tim Kaine made headlines on Meet the Press when he expressed “grave doubts” that airstrikes against ISIS in Syria were legally justified. Two days earlier, the Army it will deploy 400 soldiers to help Iraqi forces against ISIS.

Kaine’s point is not new. When President Obama announced he was deploying 50 special forces soldiers to fight ISIS in Syria last October, a bipartisan group of legislators called on House Speaker Paul Ryan to revisit Obama’s authorization to do so.

The question Kaine’s doubts reflect is an important one: Where does the war on terror stop?

If Congress thinks our current level of involvement against ISIS is unsettling, just wait. It’s only going to get worse. Democratic presidential nominee Hillary Clinton laid out a strategy more aggressive than Obama’s early on in her campaign. It’s unclear exactly what Republican nominee Donald Trump plans to do to ISIS (he doesn’t want ISIS to know what he’s planning). But, it’s safe to say whether he chooses to “bomb the hell out of them” or “take the oil”, his strategy will represent at least a measurable increase from the status quo.

What Kaine neglected to mention is the critical point: the time for Congress to reassert its mandate is now. The Obama Administration is a willing partner. It previously requested a specific authorization to fight ISIS in February 2015, including submitting a draft authorization for Congress to consider. Ultimately, no action was taken, and the status quo remained, as it has since 2001.

With the notable exception of the 2003 invasion of Iraq, all American activities to fight terrorism since the 9/11 attacks have been justified under the Authorization for Use of Military Force Against Terrorists. Passed just four days after 9/11, this act authorized the President to use force “against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks.” Later guidance would clarify this to mean “al-Qaeda, the Taliban, or associated forces.”

Until recently, it was hard to argue that ISIS was an associated force. Al-Qaeda declared war on ISIS in 2015. The Taliban has actively opposed ISIS’s expansion into Afghanistan. This disconnect, coupled with fears that American involvement in the fight against ISIS is spiraling out of control, is behind calls for a new authorization of force against ISIS in particular.

That changed on Sunday, just as Kaine was making his point. The Wall Street Journal reported that elements of the Taliban and ISIS in Afghanistan were agreeing to a series of cease fire agreements in Eastern Afghanistan. These agreements give both groups the ability to focus their efforts on fighting Afghan and U.S.-led coalition forces.

Even if the suggestion of cooperation (however informal and uncertain) is sufficient to put ISIS under the “associated forces” umbrella, it’s only a matter of time before a new, unassociated group emerges. Whoever the President is will likely stretch the same authorization from 2001 to fit that new group too. The war on terror will remain unbounded.

It may be too late to halt our ongoing engagements in Iraq and Afghanistan, but hopefully it’s not too late to control the new fronts opening up. To do so, Congress needs to take a page from Senator Kaine’s playbook and reform the War Powers Resolution of 1973.

Amid a widening Vietnam War (and over President Nixon’s veto), Congress passed a law requiring the President to notify Congress within 48 hours of deploying troops and gain Congressional approval if those troops were to be deployed for more than 60 days.

It’s an effective tool for controlling the start of conflicts, but it does nothing for our current condition: an ever-growing battle against amorphous terrorist groups.

In 2013, Senator Kaine and Senator John McCain put forth a proposal to reform the law. At the time, Kaine said, “The current resolution has been ineffective at establishing a consultative process between the executive and legislative branches of our government over our nation’s most important decision—whether or not to send our men and women in uniform into harm’s way.”

Their proposed War Powers Consultation Act of 2014 would have required the President to consult with Congress before ordering troops into a “significant armed conflict” expected to last more than seven days.

The key here is “before.” Currently, once a conflict is underway, controlling it becomes politically untenable. Congress is left in the unenviable position of taking away support from troops in harm’s way. Or, at least that’s how it was spun when Congress attempted to reign in the Bush Administration’s surge strategy in Iraq.

Kaine and McCain’s 2014 effort never progressed beyond the point of introduction. However, the bipartisan uneasiness with our level of engagement in Syria and bipartisan fears of what might be looming on the horizon, make it a perfect time to revisit the bill.