After the horrific attack in Nice, France that left at least 84 dead, Donald Trump called into various news programs, including the O’Reilly Factor, essentially calling for Congress to declare war on ISIS.

“I would, I would,” Trump told Bill O’Reilly when asked if he would declare war on the Islamic State. “This is war. If you look at it, this is war. Coming from all different parts. And frankly it’s war, and we’re dealing with people without uniforms. In the old days, we would have uniforms. You would know who you’re fighting.” At this point, it is unclear which group is behind the attack in France. Trump also added that he would use NATO to initiate war against various terrorist groups. Clinton on the other hand framed her approach to terrorism in a different way.

“It’s clear we are at war with these terrorist groups and what they represent. It’s a different kind of war, and we need to be smart about how we wage it and win it,” Clinton said on CNN Thursday night.

Trump made a bold call. And what he appears to be advocating for is very different from the way the United States has engaged in military intervention for the last several decades. Believe it or not, Congress hasn’t declared war for 74 years. In fact, according to the Senate’s historical site, Congress has only declared war on 11 occasions with the last formal declaration dating back to World War II.

The Constitution grants Congress with the sole power to declare war. Article I, Section 8, Clause 11 specifically states:

[The Congress shall have Power…] to declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water;

Since World War II, Congress has authorized military force on numerous occasions without officially declaring war.

Following 9/11, Congress passed The Authorization for Use of Military Force Law (AUMF) to fight Al-Qaeda. The law has been used broadly to authorize military engagement in hostile regions against terrorists. In fact, last year, Congress rejected Obama’s new proposal for authorization for the use of military force to battle the Islamic State in Iraq and Syria. So the President has been forced to use an outdated version of AUMF from 2001 as his legal justification for continued engagement. The administration’s argument is that since ISIS originated from Al-Quada, the post 9/11 Congressional authorization to use “necessary and appropriate force” against those that aided the terrorist attacks still applies. That legal reasoning has been the subject of much controversy.

Can he do that? In the absence of an official authorization, Army Capt. Nathan Michael Smith sued the Obama Administration in May saying the U.S. lacks legal authority to wage war on ISIS.

“How could I honor my oath when I am fighting a war, even a good war, that the Constitution does not allow, or Congress has not allowed,” he wrote in a court paper.

The Obama administration responded in a brief: “The president has determined that he has the authority to take military action against ISIL, and Congress has ratified that determination by appropriating billions of dollars in support of the military operation.”

As you can see this is a very contentious legal issue that Trump has now officially weighed in on. There are many who believe Congress can authorize a war without officially declaring it, while there are still others who say no U.S. President since F.D.R. has “respected the Constitution sufficiently to seek a formal declaration of war.”

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