The deepening depravity of the Islamic State of Iraq and the Levant (ISIL) can be read in recent headlines — or seen in grisly videos released by the terrorist group.

The latest crime came not from ISIL strongholds in Iraq or Syria, but from the failed state of Libya. On the shores of the Mediterranean, ISIL beheaded 21 Coptic Christians from Egypt. This obscenity capped a month of carnage, including confirmation of the killing of American Kayla Jean Mueller; a caged Jordanian air force pilot being burned alive, and two Japanese men beheaded. There have been other multinational victims, including aid workers and journalists, and scores more Iraqis and Syrians have been killed by ISIL as it swept up broad swaths of those nations.

The globalization of ISIL’s victims and the group’s metastasizing geographic footprint demand a global response. The United States, as part of a multinational coalition, has been in the fight since summer 2014. An updated legal framework for taking lethal action is long overdue. And U.S. forces — indeed the world — should know that despite their differences, Congress and the White House strongly back their efforts.

But as with most presidential proposals, Congress seems split on President Obama’s draft authorization for use of military force. Many Democrats, in an understandable desire to keep the country out of yet another major Mideast war, fear the authorization is not restrictive enough to prevent mission creep.

Many Republicans, conversely, think it would unnecessarily limit not just Obama’s options, but those of his successor, since it would limit U.S. involvement to three years and impact the next president. Some also believe that an authorization that signals limits only emboldens an enemy that has none.

Unlike so many Beltway debates that become abstract domestically, let alone globally, this one matters. Allies, and certainly ISIL, are listening. It’s imperative to pass an authorization that sends the right signal. Here are some markers:

The three-year limit is arbitrary and unwise. First, it technically might not matter, since Obama plans to retain a 2001 authorization to use military force that Congress granted in the aftermath of 9/11, which the administration has used as the legal basis to fight ISIL. (Obama would repeal the 2002 Iraq war authorization, however.) And the three-year span belies Obama’s oft-repeated analysis that it may take years to “degrade and ultimately destroy” ISIL.

If the point of the time limit is for the next president and Congress to reassess the campaign, that should happen anyway. An artificial date isn’t necessary, especially given the fluid nature of the threat. ISIL in its current form didn’t even exist three years ago. Three years from now, the group may have become an even bigger threat or, one hopes, it could collapse in that span.

Similarly, to bar “enduring offensive combat operations” takes options off the table. There should be no rush to deploy, and Obama has been quite clear in saying he is not considering sending significant numbers of troops back into Iraq. But it’s also important that Congress not codify combat operations.

While a strong signal from the United States is needed, it should not be misinterpreted as an order. Middle Eastern nations need to know that this is their fight. “The United States really has to signal to the region that it is willing to help, but it cannot be the principal opponent of this enemy,” said Prof. Brian Atwood, former dean of the University of Minnesota’s Humphrey School of Public Affairs.

There are some encouraging signs from the region. Kurdish Peshmerga forces have already bravely stepped up and, in the case of the Syrian city of Kobani, rolled back ISIL gains. But more is needed from many nations, including an improved Iraqi army, and from nations like Jordan, which has ramped up airstrikes in response to ISIL’s killing of its pilot, and Egypt, which struck ISIL targets in Libya in response to Sunday’s massacre.

Now it’s up to the United States to show its determination. Passing an ill-considered authorization for use of military force — or not passing one at all — would weaken allied resolve and embolden ISIL.