The chairman of the House Armed Services Committee said Congress still has a "moral and constitutional responsibility" to pass a military force authorization for current operations against Islamic State militants in Iraq.

But Rep. Mac Thornberry, R-Texas, said he's not sure if lawmakers have a path to do that.

"I just don't hear many people standing up for what the president has proposed," he told reporters last week. "So we're moving beyond that. The question is what can we pass."

Weeks of lobbying from top defense officials has done little to move Congress closer to a compromise on the issue, even as U.S. military involvement in the fight approaches its eighth month.

About 2,600 U.S. troops already have been deployed to Iraq to advise and assist — but not directly intervene — in the fight against the radical insurgents.

Defense leaders have framed the need for a new military force authorization as less about legal need — White House attorneys insist existing authorizations give President Obama the right to send troops into the region — and more about the importance of a unified message from Congress.

But lawmakers are far from unified on that message.

Sitrep: Authorization for Use of Military Force (AUMF)

Defense officials have lobbied Congress for weeks to pass a military force authorization for U.S. operations against the Islamic State group in Iraq, but lawmakers are no closer to reaching a compromise.

At a House Armed Services Committee hearing last Wednesday, Republican lawmakers grilled Defense Secretary Ash Carter about perceived limitations of the draft force authorization, while Democrats fretted about the lack of parameters.

Carter bounced between the two extremes, assuring conservatives that the plan as drafted has "substantial flexibility" to respond to the growing Islamic State threat while promising critics on the other side that its vague language won't lead to "another campaign like Iraq or Afghanistan."

Defense officials have had to make that pivot during every Capitol Hill appearance on the issue, giving varied explanations of the authorization's definition of "enduring offensive ground combat operations."

Obama's draft also includes a three-year expiration date, which would require Congress to take up the debate again in 2018 if the fighting continues.

Given the difficulty in finding congressional compromise now, some lawmakers have criticized that provision as yet another limit. But others see it as critical language to ensure military operations don't continue unchecked for decades.

Sen. Bob Corker, R-Tenn., chairman of the Senate Foreign Relations Committee, already has said he's seen little support among Democrats on his panel for the White House's draft authorization, offering little interest and urgency on working with that language.

Thornberry echoed that feeling in his chamber, saying he expects House officials to look at other congressional proposals floated in recent months for possible compromise proposals.

Neither the House nor Senate Foreign Relations committees have the issue of the military force authorization on their near-term schedules.

Carter told lawmakers that he hopes Congress will act soon, but offered no timeline or deadline for when the Pentagon hopes for action.