With questions still looming over the deaths of U.S. troops in Niger, the ranking member of the Senate Foreign Relations Committee faced top Trump administration officials last week in a public hearing and warned of a “global, endless shadow war” against terror groups.

Sen. Ben Cardin’s comments to Defense Secretary Jim Mattis and Secretary of State Rex Tillerson were part of the new political battle over President Trump’s authority to target a growing roster of extremists aligned with the Islamic State and al Qaeda across Africa and the Middle East.

The Niger ambush that left four soldiers dead directed a bright spotlight on the scope of U.S. counterterrorism operations, which largely predate Trump, and has energized Senate Democrats who seek to put limits on a new president with what they criticize as a reckless and incoherent foreign policy.

“I support duration, geographic, and tactical limitations because I think it would be dangerous to give this president a blank check,” Sen. Chris Murphy, D-Conn., a Foreign Relations member, told the Washington Examiner.

The soldiers killed in Niger were advising local troops and not deployed in a combat role, but the incident has spurred debate over when, where, and how Trump can wage war against terrorists.

Those questions are now front and center after Foreign Relations chairman Sen. Bob Corker, R-Tenn., announced the committee is fashioning an authorization for the use of military force, or AUMF, that would provide a new legal basis for the fight and replace Congress’ broad 9/11-era AUMFs that were passed before the Islamic State existed.

The Trump administration has military personnel “deployed and equipped for combat” in 19 countries under current war authorizations, according to Corker. A bill laying out the president’s new authorities could be unveiled in the coming weeks, but time is growing short as the Senate’s 2017 legislative calendar winds down.

“So far, Congress has been unable to bridge the gap between those that see a new AUMF as primarily an opportunity to limit the president and those who believe that constraining the commander in chief in wartime is unwise,” Corker said.

Democrats say a new AUMF could include an expiration date, such as a bill sponsored by Sens. Tim Kaine, D-Va., and Jeff Flake, R-Ariz., that includes a five-year sunset clause, or specifically name countries where terrorists can be targeted and how Trump could deploy U.S. troops.

“Where is the range? We’ve talked in the past about ground troops, what is the geographical limitations and the time limitations,” Cardin told the Washington Examiner. “In my view, you are only going to be able to pass one that has certain limitations.”

Publicly, the Trump administration has remained cool to the idea of a new AUMF and argued, like previous administrations, that it has all the legal power it needs to fight terror groups wherever they emerge under war authorizations passed against al Qaeda in 2001 and Iraq in 2002.

Mattis and Tillerson both pushed back against limitations on those powers, making clear in their first public testimony to the Foreign Relations Committee last week that they oppose any time or geographic restrictions on the president’s counter-terror authority.

“I think they are walking a very tight line,” said Thomas Spoehr, director of the Center for National Defense at the Heritage Foundation.

The administration does not want to give any public impression that Trump’s current legal authorities under the aging AUMFs are inadequate to pursue terrorists and it is leery of supporting new legislation that could eventual be defeated, Spoehr said.

“There are some real serious down sides that they have got to be mindful of,” he said. “What they’ve got now is better than either of those two things — one, a failed AUMF vote or, two, giving the hint that the current AUMF has legally got some flaws to it.”

Mattis and the military could also face real pitfalls with Senate-imposed limits in any new authorization, especially a legislative expiration date that requires Congress to rally around and pass a new AUMF down the road, Spoehr said.

“You can’t be assured that when it comes time to renew it that there’s going to be this logical, reliable process to renew it,” Spoehr said. “We’ll get to that mark, and there will be some sort of political paralysis that is going on at the time, so the people who will pay the price for that political paralysis will be the military because they will be off in these places … and all of sudden their authority will be cut out from under them.”

An authorization targeting specific countries could be counter-productive as terror groups are pushed out of one area, such as Iraq and Syria only to sprout up elsewhere, he said.

“You don’t want to keep running across the river and get a new AUMF every time they poke their head up in a new country,” Spoehr said.

Sen. John McCain, R-Ariz., was more blunt about the administration’s position.

“They don’t want an AUMF, that’s what it’s all about, OK,” McCain told the Washington Examiner.

McCain, who is not a Senate Foreign Relations Committee member, has lately renewed his calls for a war authorization update and said he is working on his own bill with Sen. Jack Reed, D-R.I., though he declined to provide details on what limitations he may propose.

“There would not be an AUMF if there were not some limitations and reporting requirements and other activities,” he said. “Otherwise, we wouldn’t have one.”