Sen. Rand Paul released his promised bill declaring war against the Islamic State on Wednesday, challenging the White House's ability to act under existing authority and separating himself from more hawkish members of his party with strict time and ground troop limitations.

The Kentucky Republican will try to attach the proposal to the defense authorization bill likely to come before the Senate next week. Armed Services Committee Chairman Carl Levin has urged members to pass the National Defense Authorization Act under unanimous consent, without controversial amendments—such as Paul's—that could derail its passage.

"He would like to [use NDAA as a vehicle], if he's given the opportunity," said a senior Paul staffer. If the Senate fails to move the bill under unanimous consent, "you could see Rand using a procedural mechanism to get a vote on this." The aide said Paul would prefer to see a stand-alone vote on the declaration, but because that is "not realistic," the NDAA is the next-best option.

Paul's announcement comes as he and his fellow contenders for the GOP presidential nomination jockey for position on foreign policy issues. On Tuesday Paul reasserted his reluctance to take America to war and refused to pledge to increase defense spending as president. Likely 2016 rival Sen. Ted Cruz, meanwhile, called for a more aggressive U.S. foreign policy, including tough sanctions to prevent Iran from acquiring nuclear weapons and ground troops to fight the Islamic State.

Paul's urgency—addressing the issue in the lame-duck session and attempting to tie it to a key bill—springs from the fact that he believes the White House currently lacks the authority to conduct military operations against the Islamic State. The administration asserts that it has the authority to act whether or not Congress gets involved, but it has said it welcomes legislative action. Addressing the war's constitutionality "is far more important than this fight over appropriations," said the staffer.

In a statement accompanying the draft, Paul said, "This war is illegal until Congress acts pursuant to the Constitution and authorizes it." In typical Paul fashion, the document begins with a 15-line history lesson on the war-making power of the legislative branch before outlining the terms of the conflict.

Under Paul's bill, the administration would be given the authority to fight the Islamic State in Iraq and Syria. However, the draft limits the use of ground troops to rare circumstances, such as protecting Americans in danger or gathering necessary intelligence. It also sets its own expiration date a year after its passage.

In addition, the bill would repeal previous congressional authorizations for the use of military force, which the Obama administration has said give it the authority to fight terrorism in the Middle East. In a shot at the White House, Paul's bill states that the authorization passed after 9/11 "does not provide any authority for the use of military force against the organization referring to itself as the Islamic State, and shall not be construed as providing such authority."

Other senators, such as Virginia's Tim Kaine, have urged congressional action on the coming Islamic State conflict, arguing that the legislative branch should make use of the power it has as a deterrent to executive overreach. But many more lawmakers, they acknowledge, would rather not cast votes that involve putting American troops in harm's way. If Paul's proposal unleashed a flurry of rival war declarations and force authorizations, "that would be a welcome development," said the Paul staffer—as long as Congress is having the debate. Still, Levin and others worry such amendments could make passage of NDAA a muddled mess.