Chris Edelson

Opinion contributor

American politics and governance are so dysfunctional at the moment that it’s possible President Donald Trump’s baseless claim that he has authority to take the country to war with Iran without congressional approval could pass by without challenge or real debate. That would be a serious, possibly disastrous, mistake.

The Constitution provides thepresident with limited authority to order the use of military force when the country faces an actual or imminent attack. Fortunately, that is not currently the case when it comes to Iran. Under the current circumstances, Trump would need congressional authorization to proceed with a military strike against Iran.

Last week, Trump took to social media to claim that he had called off an attack against Iran at the last minute. The president separately emphasized his belief that he can act unilaterally, saying of members of Congress “I do like keeping them abreast, but I don’t have to do it legally.”

In fact, Trump is legally required — not just to inform members of Congress, but to gain their approval before he orders military action against Iran, unless an emergency makes it impossible to do so. The legal authority here is the United States Constitution, which assigns Congress the power to declare war. The Constitution gives the president no explicit authority to use military force without congressional approval.

No 'sudden attack' that demands response

There is evidence from the debate at Philadelphia in 1787 that the drafters of the Constitution intended for the president to have implied authority to “repel sudden attacks.” That makes sense, of course. In an emergency, with no time to gain congressional approval, a president should be able to defend the nation against an actual or imminent attack.

More on Iran:A wobbly Donald Trump decided not to strike Iran. We should be glad.

Fortunately, there have been very few times in American history when this kind of emergency unilateral presidential action was necessary. The only clear example is at the start of the Civil War. With Congress out of session and a number of states engaged in open rebellion against the United States, President Abraham Lincoln took unilateral action, including ordering a naval blockade and suspending habeas corpus between the nation’s capital and Philadelphia. Lincoln later asked Congress to retroactively approve his actions, forthrightly acknowledging that some of what he had done may not have been “strictly legal,” but that he had acted out of necessity.

For nearly 100 years, presidents did not break with Lincoln’s example. That changed with the Korean War when President Harry Truman ordered a large scale military operation — war under any reasonable meaning of the word — without congressional approval. Congress could have acted to stop him, but it did not.

Violations from Reagan to Clinton to Obama

As a result, presidents since Truman have been emboldened to order military action in situations where the United States did not face an actual or imminent attack — from Ronald Reagan in Grenada to Bill Clinton in Bosnia and Barack Obama in Libya. Each of these presidents was violating the Constitution. They were only able to act because members of Congress abdicated their constitutional responsibilities. The fact that these presidents were able to get away with illegitimate action does not provide good precedent for presidents hoping to build on past constitutional violations.

Some defenders of presidential authority point to the War Powers Resolution to support the case for presidential power. This is a misconceived argument.The resolution is poorly drafted and internally contradictory. Part of the law seems to provide that presidents can only act unilaterally in an emergency, when the United States or its armed forces are attacked. Another part suggests presidents can enter into “hostilities” for a limited period of time (60 or 90 days) even when there is no emergency scenario.

Fortunately, it is not necessary to sort out this confusing statutory language. The resolution is a statute, and as such, it cannot expand or contract presidential authority under the Constitution. To the extent that it is cited as authority for the president to unilaterally order the use of military force outside of an emergency, such a claim would be unconstitutional.

More Iran commentary:Why a war with Iran is unlikely: Donald Trump calls the shots and he doesn't want one

As we have frequently been reminded over the past few years, constitutional limits on presidential power are not self-executing. In most cases, members of Congress are best positioned to enforce these limits — which means that, when they fail to act, the president is allowed to self-regulate (a “limit” with little meaningful value).

Recent history reminds us, however, that members of Congress can be moved to act — and that when they do, they can stop presidents from going to war unilaterally. In 2013, with Obama poised to order military action against the Assad regime in Syria, more than 100 members of Congress signed a letter making clear that Obama needed legislative approval to strike. Obama decided not to act.

There are members of Congress today, including Republican Rep. Justin Amash of Michigan and Democratic Sen. Jeff Merkley of Oregon, who have publicly rejected Trump’s claim that he can order a military strike against Iran at his discretion.The question is whether others in Congress will join them in enough numbers to make a difference. If they don’t, legislators will once again surrender their constitutional authority — this time, to a president who could easily stumble into a conflict beyond his comprehension or ability to control.

Chris Edelson is an assistant professor of government in American University’s School of Public Affairs. His latest book is “Power without Constraint: The Post-9/11 Presidency and National Security.” Follow him on Twitter: @ChrisEdelson