Trump and Obama shake hands in the Oval Office. Kevin Lamarque/REUTERS The Obama administration recently expanded a 15-year-old congressional authorization for the use of military force (AUMF) to include members of the African Islamist militant group al-Shabab, The New York Times reported earlier this week.

The AUMF was passed shortly after the September 11, 2001, terror attacks, authorizing the US military to wage a global war on Al Qaeda and "associated forces" — a provision that has allowed the Obama administration to bypass new authorization from Congress for operations targeting militants in Libya, Yemen, and now, Somalia.

Obama's characterization of the Islamic State — and now, of al-Shabab — as an "associated force" of Al Qaeda has been controversial, with many experts warning that it is a slippery slope to a forever war.

"The potential for the war to expand around the world cries out for a genuine expiration date," Ryan Goodman, an expert on international law and member of the Council on Foreign Relations, wrote last year. "The next administration should know that it will have to justify its own choices when the time comes for renewal."

Some analysts fear, however, that the incoming administration of President-elect Donald Trump will inherit vastly expanded war powers under Obama's elasticized AUMF. They say it could encourage Trump to preserve the tradition of bypassing congressional approval for combat operations against Islamists.

“It’s crazy that a piece of legislation that was grounded specifically in the experience of 9/11 is now being repurposed for close air support for regional security forces in Somalia,” Micah Zenko, a senior fellow at the Council on Foreign Relations, told The New York Times.

"This administration leaves the Trump administration with tremendously expanded capabilities and authorities," he added.

Trevor Timm, executive director of the Freedom of the Press foundation, tweeted on Monday that "everyone's freaking out about Trump, but not many seem to care Obama is unilaterally expanding war powers for him."

'They're happy to give him carte blanche'

It's unclear whether Obama's expansion of the AUMF to include al-Shabab would give Trump war powers he wouldn't have already under the legislation.

While Obama has demonstrated that the president doesn't actually need new congressional approval to launch combat operations against Al Qaeda's "associated forces," Congress' role in overseeing the war on terror has been limited by its inability to pass new legislation that delineates its constraints.

Last year, for example, lawmakers voted to approve funding for the war against ISIS, but avoided specifically authorizing the war under a new AUMF.

"I suspect the Trump administration may be inclined to a very expansive reading of [AUMF] authorities, whether Obama establishes this precedent or not," Stephen Biddle, an adjunct senior fellow for defense policy at the Council on Foreign Relations, told Business Insider.

"Real capability of the next president may be more decisive than interpretations of legal authority," he said.

Lindsey Graham proposed in January that the President be authorized to "use all necessary and appropriate force" — including ground troops — against ISIS and associated forces. Mohamed Abd El Ghany/Reuters

Incidentally, the Trump administration's capabilities could be broadened both practically and legally not by Obama but by Republican Sen. Lindsey Graham, a hawk who was one of Trump's harshest critics along the campaign trail.

The South Carolina senator proposed in January that the president be authorized to "use all necessary and appropriate force" — including ground troops — against ISIS, its "associated forces," and any "successor organizations," without an expiration date.

Senate Majority Leader Mitch McConnell — who, along with other Senate Republicans, had been reluctant to "tie the president's hands behind his back" with a new AUMF that might constrain rather than expand war powers — surprised when he fast-tracked the bill for a debate.

The Obama administration and Democratic senators, meanwhile, have pushed for a narrower AUMF that does not include ground forces and would expire after three years.

"Some of the same House and Senate members who are so critical of this so-called imperial president [Obama] are ready to make him an imperial president when it comes to war-making,” Democratic Rep. Adam Schiff, the ranking member on the House Intelligence Committee, said last year. “They’re happy to give him cart blanche.”

But they didn't end up giving that to Obama — Graham's proposal has yet to come to a vote.