Seven months after the first U.S. airstrikes against the Islamic State militant group, President Barack Obama is set to ask Congress to sign off on the campaign and provide legitimacy to his actions. On the face of it, getting lawmakers to approve military force against the group -- formally known as an Authorization for Use of Military Force -- would appear to be an easy victory. But not with this Congress.

“There is a heavy political dimension to this,” said Kenneth Gold, director of the Government Affairs Institute at Georgetown University. “Even as recently as 2001 and 2002, there was pretty much bipartisan consensus on something like this, that this wasn’t a partisan political issue. Now it’s overwhelmingly a partisan issue and it’s because of how dramatically more partisan Congress is now than it was 10 or 15 years ago.”

In today’s political climate, where more conservative elements of the Republican Party have greater clout in the House of Representatives, there will likely be some congressmen who will vote against a new AUMF simply because it’s Obama who is pushing for it. And hawks like U.S. Sens. John McCain, R-Ariz., and Lindsey Graham, R-S.C., want the option to expand the military campaign against the militant group also known as ISIS beyond airstrikes.

"The challenge we're seeing right now is that Congress is staking out a position that is far more hawkish than what the administration might want in an AUMF," said Dan Mahaffee, vice president and director of policy at the Center for the Study of the Presidency and Congress in Washington, D.C. "The Republicans are very keen to be able to allow more boots on the ground or for more of a combat role."

Meanwhile, Democrats are concerned about giving unlimited duration to the authorization after the war in Iraq stretched out, while Republicans generally hold the view that Congress shouldn't limit a president's power as commander in chief. This means it will be difficult for Obama to get the authorization he wants with all these competing views.

"Lawmakers don’t want their fingerprints on something that could go poorly and that could put Americans in harm's way," said Sarah Binder, a senior fellow and expert on Congress and legislative politics at the Brookings Institution and professor of political science at George Washington University in Washington, D.C. "There's an almost impossibility to see a path forward to this, absent some change on the ground."

For years, AUMFs have been standard operating procedure for how military force is authorized. While Congress has the power to declare war, it hasn’t done so since World War II. But there have been nearly 150 AUMFs signed off on since then. Declaring war on ISIS is not a realistic option.

"The traditional explanation is declarations of war were against sovereign states. The argument in this case would be not to legitimize the Islamic State," Gold said.

In 2001 and 2002, Congress overwhelmingly gave then-President George W. Bush approval for military action against al Qaeda and Iraq. Both AUMFs have no expiration date, and Obama has used both authorizations as justification for the U.S.-led coalition strikes against ISIS. 

“I think the main thing is that Congress is very leery about getting into a new [AUMF] because the last two have been indefinite in their duration,” said Don Wolfensberger, a congressional scholar at the Woodrow Wilson International Center for Scholars in Washington, D.C. “I think it’s the war wariness that people have and that concern that this is going to end up escalating.”

That’s part of the reason Obama wants Congress to approve an authorization even though he argues that he had the authority to greenlight the airstrikes against ISIS as commander in chief. “For the president, it’s political cover to try to get Congress to buy into this and therefore, if things go badly, to share the blame on this,” Gold said.

Obama has ruled out using ground troops against ISIS, but House Speaker John Boehner, R-Ohio, wants the AUMF to be broad enough to give Obama that option should circumstances change. Secretary of State John Kerry also has argued for the AUMF to give Obama wide-ranging authority, including not limiting the authorization to just striking ISIS in Iraq and Syria.   

As far as a sunset provision, negotiations between Congress and the president point to a three-year expiration for the new AUMF, according to House Minority Leader Nancy Pelosi, D-Calif., the Associated Press reported. While other details have yet to take shape, Pelosi said she believed Congress will give Obama authorization.

"I'm not saying anybody's come to an agreement on it," Pelosi said, according to the AP. "I think it's going to be a challenge, but we will have it."