The United States Senate has voted in favour of invoking its war powers to force President Donald Trump to halt his military campaign against Iran or seek congressional approval before any further action is taken.

Here is a closer look at Tuesday’s vote – the 10th attempt Congress has made to rein in the US-Israel war on Iran – and what this means for the US government.

Why did this vote take place?

A similar measure had already been approved in the House of Representatives on June 3 by a vote of 215 to 208, and on Tuesday, the Senate passed it in a 50-48 vote. Trump’s Republican Party has slim majorities in both chambers.

Speaking on the Senate floor before the vote, top Democrat Chuck Schumer advocated for the war powers resolution as he criticised Trump’s military campaign against Iran.

“For years, Trump promised to put maximum pressure on Iran, but he ended up delivering maximum confusion, maximum chaos, maximum cost to the American people with his disastrous war,” Schumer said.

“Time after time, the vast majority of Senate Republicans sided with Trump and his war instead of the American people. The American people have paid the price for Trump’s historic blunder in Iran. It’ll go down in the history books as one of the worst foreign policy forays America has ever made.”

The war against Iran has proved highly unpopular in the US. A poll released on Tuesday by the news agency Reuters and the research firm Ipsos found that 24 percent of respondents felt the war had been worth the cost.

The Senate passed its first war powers resolution against the Iran conflict on May 20, but that effort was a procedural move only and did not progress.

Who voted and how?

Four Republican senators crossed party lines to vote for the resolution, and all but one of the chamber’s Democrats also voted in favour.

Tuesday’s breakaway Republicans were Bill Cassidy of Louisiana, Lisa Murkowski of Alaska, Susan Collins of Maine and Rand Paul of Kentucky. A further two Republicans did not vote: Mitch McConnell of Kentucky and Dave McCormick of Pennsylvania.

The lone Democrat to vote against the measure was Pennsylvania’s John Fetterman.

What does the resolution say?

The war powers resolution “directs the President to remove United States Armed Forces from hostilities against the Islamic Republic of Iran”.

Only if “explicitly authorised by a declaration of war or a specific congressional authorisation” would Trump be allowed to use further military force against Iran, it says.

The resolution, however, does allow for a limited military presence to remain in the Middle East to prevent any “imminent attack” against the US or its allies.

What is the significance of the vote?

The vote reflects growing unease even among some of Trump’s Republican supporters about the unpopular conflict, which began with US-Israeli air strikes on Tehran on February 28.

This is the first time both chambers of Congress have passed a resolution directing a president to remove US armed forces from a warzone under the War Powers Act although it was not immediately clear how the votes might affect the conflict.

Technically, the Trump administration should now seek explicit congressional approval for further strikes on Iran. However, previous administrations have found routes around this by securing more limited authorisations for the use of military force (AUMFs) instead.

For example, in the wake of the 9/11 attacks in 2001, Congress passed an AUMF that gave then-President George W Bush broad powers to conduct what would become the global “war on terror”.

And one year later, it passed another AUMF, allowing the use of the military against the government of Saddam Hussein in Iraq, which became the basis of the 2003 invasion.

The two authorisations remain in place, and presidents continue to rely on them to carry out strikes without first seeking congressional approval. The assassination of top Iranian General Qassem Soleimani in 2020 in Baghdad was authorised by Trump under the 2003 AUMF.

In addition, a resolution does not have the force of law. Experts said, therefore, that while the Senate vote is viewed as a rebuke to Trump, it is largely symbolic.

What effect will this have on US-Iran talks in Switzerland?

Before the vote on Tuesday, some Republican senators had warned that the war powers resolution would weaken Trump’s standing in the Switzerland negotiations.

“If this passes, the Iranians are going to simply stand up and walk away from negotiations,” Senator James Risch of Idaho told the Senate on Tuesday.

“They’re going to say: This thing’s over. The Congress has told the president of the United States, ‘Leave us alone. We can do whatever we want to do,’ and they will walk away.”

How will the Trump administration respond?

Risch also argued that the resolution is essentially useless, given its symbolic nature. “It’s going to have no effect. The president isn’t going to pay any attention to it,” he said.

The US Constitution gives Congress the sole power to declare war, but that division of power has eroded over the past 75 years as successive presidents alone have committed US forces to overseas conflicts.

Trump has pointed to that precedent to argue that he does not need congressional authorisation at all.

In an appearance on The Axios Show last week, Trump denied learning any “lesson” about the limits of his executive powers during the Iran war. “There are no limits,” he said.

The last time Congress voted to go to war was during World War II although it has passed AUMFs in the decades since, which allow for limited military engagement without congressional approval for all-out war.

During Trump’s first term, there were concerns that he could use the 2001 AUMF to strike Iran under the unfounded claim that Tehran supports al-Qaeda.

Some critics pointed out that Republicans may be more willing to confront Trump over the issue of congressional authorisation now as they defend their seats before November’s midterm elections.