A Democratic senator who has long called for Congress to take a more active role in decisions to authorize U.S. military action around the world is expressing concern about the Trump administration’s view of “collective self-defense.”

Virginia Democratic Sen. Tim Kaine released a letter Wednesday to Defense Secretary James Mattis indicating that there are very few limits on the scope of self-defense under interpretations of current law.

“The collective self-defense supplemental rule of engagement, when approved, permits U.S. forces to defend partner forces from attack or an imminent threat of attack with necessary and appropriate force, and typically the authority applies irrespective of the group or individual committing the hostile act, or demonstrating hostile intent,” the Defense Department said in a reply to Kaine about previous questions, according to Kaine’s letter.

“As such, collective self-defense is not typically limited to particular groups or individuals committing the hostile act or demonstrating hostile intent, including not being limited to groups covered by the 2001 AUMF or other congressional authorizations for the use of force,” the reply to Kaine said, much of which appears to remain classified.

“I am alarmed that the Department of Defense believes that, by merely designating a group as a partner force, it can respond with military action to protect that partner force and its property if threatened by any group — even one that poses no direct threat to the United States, its Armed Forces or persons, nor is covered by an AUMF,” Kaine wrote in his Wednesday letter.

Kaine has been an at times lonely voice in supporting a new use of force authorization to supplant the two authorizations adopted in 2001 and 2002, which continue to form the legal basis for much of U.S. involvement in the Middle East.

Kaine teamed up with Foreign Relations Chairman Bob Corker of Tennessee and some senators from both parties to unveil a new AUMF back in April. But, perhaps unsurprisingly, there has been no hint of a chance for floor debate on their proposal or any competing proposal.

According to Kaine, what he has now been told by the Defense Department under President Donald Trump goes even beyond those old authorizations.

“I view the use of collective self-defense as yet another unilateral expansion of the President’s Article II authority in a now 17-year counterterrorism campaign that seemingly knows no limits or end,” Kaine wrote. “I am also troubled that it appears the Department has not appropriately notified Congress, as required by law, of instances in which U.S. forces have acted ‘in self-defense or in defense of foreign partners’ outside a declared theater of active armed conflict.”

The letter to Mattis was dated Tuesday.

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