"I introduced a resolution reasserting that Article 5 of the NATO Treaty does not supersede Congress's responsibility to declare war or authorize military force before engaging in hostilities," Paul wrote in Responsible Statecraft.

NATO's Article 5 outlines mutual defense commitments of the 31-member alliance but does not automatically mean the US must intervene militarily if a NATO ally comes under attack.

"For decades, many legislators have incorrectly interpreted Article 5 as an obligation that unquestionably commits the United States to provide military support should a NATO ally be attacked," he wrote.

Article 5 states: "The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force."