[This article first appeared at Politix.com.]

It’s well known that the power to declare war is left with Congress in Article 1, Section 8 of America’s constitution. With that in mind, how can Obama unilaterally attack Syria without congressional approval? The answer is, he can’t, not without an imminent threat to the US, and that becomes especially clear when you look at what America’s founders had to say about war powers. Washington, Madison, Jefferson, Adams, and Hamilton all agreed that the power to declare war belongs absolutely to Congress, and not to presidents.

In the wake of Assad’s alleged use of chemical weapons in Syria, it has been reported that the White House was planning on responding with military force without congressional approval. But as congressional opposition began to mount, and a vote in the UK failed, then President Obama ultimately decided to involve Congress in the decision. All the while, the White House and Secretary of State John Kerry have maintained that the president has the authority to use force with or without the approval of Congress, and even if Congress were to vote down approval. (This is in significant contrast to in the UK where once the parliament voted down military action the Prime Minister acknowledged that he could not act.)

In the arena of war powers, Congress’s constitutional role is not merely one of oversight.*** The US cannot initiate a war without affirmative action from Congress, other than in exigent circumstances that may require immediate action (if the US is attacked). Congress is not fulfilling its constitutionally-appointed role if it merely assumes an oversight position, with a select few Congress members being informed of ongoing military activities either through statute or through informal practices. Failure to act is itself the equivalent of a constitutionally enabled congressional “veto.” As explained by Alexander Hamilton, a strong Federalist:

The plain meaning [of the power to declare war] is, that it is the peculiar and exclusive province of Congress, when the nation is at peace to change that state into a state of war; whether from calculations of policy, or from provocations, or injuries received: in other words, it belongs to Congress only, to go to War.

Ultimately, the power to declare war is left with Congress in Article 1, Section 8. Additionally, Congress has the power of the purse, granting Congress the authority to continue or suspend military actions through funding decisions. Congress can effectively end a war by eliminating federal funding for such hostilities.

Post-founding statements and practices provide clearer evidence in support of the view that congressional authorization is constitutionally required for some uses of force. When the United States faced attacks from Native Americans along the western frontier, President Washington consistently denied that he had the power to engage in offensive military actions in the absence of congressional authorization:

The Constitution vests the power of declaring war with Congress; therefore no offensive expedition of importance can be undertaken until after they have deliberated on the subject, and authorized such a measure.

President John Adams explained a similar attitude towards presidential war power with respect to the undeclared war with France in 1798. President Thomas Jefferson took a similar view, at least in his public statements, with respect to attacks by the Barbary Pirates in 1801-1802.

James Madison took the same stance and gave a compelling reason why the constitution is framed that way. The president should not be in charge of war powers, he wrote to Jefferson in 1798, because “the Executive is the branch of power most interested in war, and most prone to it. It has accordingly with studied care vested the question of war to the Legislature.” Jefferson concurred: the legislature will keep a tighter leash on the “dog of war” than will the executive branch, and so only the legislature was granted “the power of letting him.”

But over the course of the twentieth century, presidents abandoned this historical and constitutional restraint. The Korean War and Vietnam War, in particular, demonstrated that the executive branch appeared to have usurped the authority to start war without congressional involvement.

In 1973, in the aftermath of Vietnam, Congress passed the War Powers Resolution, overriding President Nixon’s veto. The resolution was intended to “fulfill the intent of the framers of the Constitution of the United States and insure that the collective judgment of both the Congress and the president will apply to the introduction of United States Armed Forces into hostilities.” While the Constitution establishes a number of powers that are clearly enumerated to Congress in the realm of foreign affairs and defense, today, as a result of Congress’s abdication of responsibility, the War Powers Resolution (WPR) remains one of the few tools that Congress has to limit presidential war-making powers. (However, it should be noted that many, particularly on the right, dispute the WPR’s constitutionality).

Despite the enactment of the WPR, presidents since Nixon have undertaken a large number of military actions without congressional approval. These include military deployments in the bombing of Libya in 1986, the conflict in Panama in 1989, the deployment into Somalia in 1992, the deployment into Bosnia in 1995, deployments into Serbia in 1999, and attacking Libya in 2011.

Often the president has claimed constitutional authority and bypassed the WPR by asserting that “limited operations” do not require congressional authorization. In the case of Libya, the definition of limited operations was stretched to a potentially unprecedented level of activity. The White House claimed that a sustained air campaign to destroy various military targets, enforcement of a no-fly zone and a no-drive zone, and clandestine assistance on the ground were not a “war” in “the Constitutional sense.” According to State Department Legal Advisor Harold Koh in his testimony before the Senate Foreign Relations Committee, the Libya operation did not constitute the kind of “hostilities” envisioned by the WPR because:

1) “The mission is limited”

2) “The exposure of our armed forces is limited”

3) “The risk of escalation is limited”

4) “The military means we are using are limited.”

Harold Koh’s reading of the WPR appears to be based upon the premise that the WPR was designed to protect against large numbers of armed service members being deployed in ground combat in another country, as in Vietnam. The WPR makes no such distinction: rather it is designed to prevent unlawful and unconstitutional wars, not merely to protect armed service members from ground combat.

Thankfully, there’s another more powerful mechanism protecting armed service members from unnecessary ground combat: public opinion. Whenever members of our armed services get deployed abroad, all Americans worry for their safety, and if the armed service members are deployed for little or no reason relevant to US national security and placed in danger, then the American public can and has placed pressure to pull out of that conflict. The American people generally grow war weary of such conflicts.

However, there are ways that a war without boots on the ground is more dangerous than one involving ground combat (while safer for the service members). Such a war can stay out of sight and out of mind because our sons and daughters are not deployed in a war zone. Such ‘invisible’ wars can go on for decades without the American people having the same revulsion as they would for a war in which our service members are deployed. Invisible wars may be no less costly to civilians on the ground on the other side of the conflict, and just as dangerous in terms of potential blow-back for America. Modern cruise-missiles and strategic bombing have allowed for much of this “invisible war,” and now cyber weapons and drone strikes are taking this to a whole new level.

In a soon-to-be-real world in which drones are sophisticated and omnipresent in the battlefield, would many forms of ‘future war’ be beyond the War Powers Resolution’s reach? By the Obama administration’s Office of Legal Counsel interpretation, cyber-attacks would almost definitely be considered a limited military action based upon the “nature, scope and duration” of the use of force (and according to reports they may be part of an attack against Syria).

Our country has steadily made the process of going to war much easier for the executive branch by transitioning to a volunteer army, maintaining base deployments around the world, and investing in a military that is many orders of magnitude superior to every other military in the world. Cyber weapons may continue to make the prospect of war that much easier.

None of these changes making war easier for presidents are specifically targeted by the WPR, but that shouldn’t matter. The resolution was designed for much more than ensuring that combat troops are not deployed abroad: it was designed to make war a difficult decision that had to be explained to the American people and a decision that required the approval of their representatives through Congress.

The constitution was written for the ages, and Congress has an affirmative duty to ensure that its system of checks and balances is not negated by the passage of time and new technologies. Congress must actively assert itself because the courts are often unable to enforce the institutional checks and balances between the branches. If Congress fails to actively asserting its prerogative in this arena, it is complicit in the president’s actions to usurp its constitutional role. (For more on Congress’s failure, see my previous brief).

Our Founding Fathers were especially fearful of a Commander in Chief with unlimited war-making power, which is why our system of checks and balances between the legislature and executive requires a congressional role in foreign affairs and decisions relating to war. Perpetual war was known to be an existential threat to liberty. For these reasons the critical instruments of war-making power were placed in the hands of Congress – principally through the power of the purse and the power to declare war.

The constitution vests the power of declaring war in Congress; therefore no offensive expedition of importance can be undertaken until after they shall have deliberated upon the subject and authorized such a measure (President Washington, 1793).

*** Perhaps the best source to understand the Congressional role in war-power vis-à-vis the President can be found in the Pacificus-Helvidius debates of Alexander Hamilton against James Madison. While debating the Constitutionality of President Washington’s decision to issue a statement of neutrality in regard to ongoing hostilities between France and Britain, these two founders provide significant depth to understanding what was meant by the Constitutional text. While the founders clearly didn’t agree, Alexander Hamilton was the federalist in favor of the most executive power, for that reason quotations by him were chosen above. To even among the most federalist oriented of our founding fathers, Congress’s role in war-making was much more significant than mere oversight of the executive. These debates can be found here.

Derek Khanna (@DerekKhanna and Facebook.com/derekkhanna) is the maverick former Republican staffer and civil liberties advocate whose op-eds on cell phone unlocking went viral in January. He is now a Yale Law Fellow, columnist, and policy expert, and leader in the campaign to legalize unlocking your cell.