Congress has not voted on an authorization for the use of military force for the conflict against the Islamic State, which began last summer. (Bill O'Leary/The Washington Post)

As U.S. military operations against the Islamic State in Iraq and Syria approach the one-year mark, a bipartisan pair of senators have launched an attempt to force Congress to provide the administration with specific authority for the fight.

Sens. Timothy M. Kaine (D-Va.) and Jeff Flake (R-Ariz.) chastised fellow lawmakers as ducking their responsibility to debate and vote on an authorization for the use of military force (AUMF) for a conflict that began last summer.

“Let’s face it, our allies and our adversaries and . . . the troops . . . need to know that we back the mission,” Kaine said in a briefing for reporters Wednesday.

Kaine and Flake, who introduced an AUMF bill Tuesday, said they were heartened by indications from Senate Foreign Relations Committee Chairman Sen. Bob Corker (R-Tenn.) on Tuesday that the panel will discuss the issue before Congress recesses next month for the summer.

“Prior to yesterday, we had no commitment at all to discuss this in any fashion,” Flake said.

Efforts to pass an authorization have languished over the past year as Democrats and Republicans split on how much leeway they wanted to allow President Obama to conduct operations against the Islamic State.

Democrats, noting the expansive powers that both Obama and his predecessor, George W. Bush, claimed under the 2001 AUMF to fight al-Qaeda, have tried to limit presidential prerogatives in the current fight by imposing sunset provisions and strict prohibitions on the use of ground troops in what so far has been largely an air campaign.

Republicans have insisted that those limits would tie U.S. hands in prosecuting a counterterrorism war that they and Obama have said is important to U.S. national security.

When he began the airstrikes last August in Iraq, and in Syria in September, Obama said they were legally justified under the 2001 authorization because the Islamic State’s leadership had its roots in al-Qaeda-linked operations in Iraq nearly a decade ago. But he said he would welcome an authorization specific to the Islamic State.

For months, the White House and Congress went back and forth over which of them should craft new legislation.

After extensive consultations with lawmakers, Obama in February proposed wording designed to split the difference between deeply divergent partisan views. His proposal would authorize military force for three years against the Islamic State and “associated forces” while prohibiting “enduring offensive ground combat operations.”

It defines “associated forces” as those “fighting for, on behalf of, or alongside ISIL or any closely-related successor entity” against the United States or its coalition partners. ISIL is one of several acronyms for the Islamic State.

The bill introduced by Kaine and Flake has many of the provisions that are in Obama’s proposal, but it changes the ground troops wording to say that “the use of significant United States ground troops . . . except to protect the lives of United States citizens from imminent threat, is not consistent” with the authorization.

It also expands the definition of “associated forces” to include direct threats to “forces trained by the coalition, in their fight against ISIL.”

Kaine said that that provision is intended to permit the United States to help defend moderate opposition forces in Syria that are engaged in the fight against the Islamic State should they come under attack by the forces of Syrian President Bashar al-Assad.