By Carlo Muñoz - 07/25/13 06:14 PM EDT
In particular, Levin grilled Preston on how he characterizes "associated forces," or terror groups loosely affiliated with al Qaeda and other radical Islamic organizations.
Critics claim the wide definition of associated forces gives U.S. military and intelligence officials carte blanche to carry out clandestine strikes against those individuals, with little to no evidence of their actual involvement in terrorist operations.
The definition allows a "frightening amount of power and it is counter to the rights enshrined in the United States Constitution," House Armed Services Committee Ranking Member Rep. Adam Smith said in June.
House defense lawmakers earlier this year passed legislation to rein in how military and intelligence officials use the associated forces definition.
The House-mandated review, included in its version of the fiscal 2014 defense authorization bill, requires the Pentagon to specifically lay out whether so-called associated forces are directly tied to al Qaeda operations.
The Department of Defense must also prove those forces are engaged with ongoing or future terror plots against the United States or its allies, according to the House language.
But on Thursday, Preston told Senate defense lawmakers the associated forces rule, as written, already has the right amount of restraints built into it.
"My understanding of the concept of associated forces is that it is quite narrow," according to Preston.
The associated forces rule allows individuals or groups to be targeted by U.S. forces only if they have "entered the fight alongside al Qaeda ... in hostilities against the United States and its coalition partners," he said.
"It's not [just] any group that is ideologically aligned with al Qaeda," Preston added.
Levin and Sen. John McCain (R-Ariz.) had planned to introduce language in the Senate defense panel's version of the fiscal 2014 defense bill to address the associated forces rules.
But panel members ended up ducking the issue entirely when the full committee approved their defense authorization bill in June.