Does Trump have the authority to declare war on Iran?

US Constitution and technicalities create an often-debated grey area

The prospect of the US assisting Israel in attacking Iran has renewed an old constitutional debate. Reuters

President Donald Trump's announcement that he would make a decision in two weeks about whether to directly involve US forces in Israel's war on Iran has reignited a longstanding constitutional debate on exactly what military powers America's leader has.

The President has indicated in recent days that the US could carry out strikes against Iran in support of its ally. Israel began attacking Iran on June 13, saying it aimed to prevent its archenemy from developing nuclear weapons. Iran retaliated with missile and drone strikes on Israel.

According to the US Constitution, it's the Congress - the House of Representatives and the Senate - that has the power to declare war.

This stretches back to 1973, when Congress passed the War Powers Act - also referred to as the War Powers Resolution - which sought to prevent the executive branch from declaring war without congressional approval. It was initiated shortly after a series of presidents unilaterally escalated the Vietnam war, specifically when Richard Nixon ordered the bombing and invasion of Cambodia without a green light from Congress.

The War Powers Act, more commonly referred to as the War Powers Resultion, sought to give US Congress more authority in declaring war. US National Archives

Yet there are several loopholes that various US presidents have used since the passage of the War Powers Act to exercise their ability to influence military policy.

There's nothing in the legislation that prevents the White House from assisting other countries, with the current example being Israel.

Some legal experts have also pointed out that the US Constitution, specifically Article II Section 2, states that "[the] President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States" - that is, the White House has a legal precedent to try and mobilise the US military to some extent.

"There is a constitutional ambiguity between the role of Commander-in-Chief and the congressional power to declare war," said Timothy Kneeland, a professor of history, politics and law at Nazareth University in upstate New York.

US Marines stand guard at the Westwood Federal Building complex as demonstrators protest against US involvement in the conflict between Israel and Iran. AFP

Prof Kneeland said that shortly after the September 11, 2001, terror attacks, George W Bush, president at the time, sought and obtained authorisation from Congress to use military force in both Afghanistan and Iraq,

These so-called Authorisations to Use Military Force (AUMF) have since been used to justify actions against ISIS and Hezbollah, as well.

"It may be that President Trump will use this as a pretext should he decide to attack Iran, which has been identified with supporting Hezbollah, listed as a terrorist organisation in the US," Prof Kneeland said, noting that laws passed after 9/11 blurred clarity on who could declare war.

What the Israel-Iran war means for the Middle East, nuclear escalation and the global economy

What the Israel-Iran war means for the Middle East, nuclear escalation and the global economy

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It could also be a matter of semantics, with the US providing assistance to Israel without ever mentioning war.

Yet there is already pushback from Democrats and Republicans, as politicians seek to head off any potential unilateral decision by Mr Trump to move ahead with military action against Iran.

In the Senate, Democratic Senator Tim Kaine introduced a resolution seeking to make debate and a vote compulsory before any military strike on Iran. And in the House of Representatives, Republican Thomas Massie introduced a similar resolution related to the situation in Iran.

Yet resolutions like this, compared to laws, often lack enforcement mechanisms.

Prof Kneeland also points out that constitutionally, Mr Trump could easily block them.

"These are subject to President Trump's veto power and would require a two-thirds majority to override the presidential veto," he said. "With both the House and Senate in the hands of the Republicans, who overwhelmingly support President Trump, this seems highly unlikely."

So, even with the 1973 War Powers Act, the ball appears to be in Mr Trump's court.

Iran, meanwhile, is holding talks with European powers as its war with Israel enters a second week.