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The crisis in the Middle East was the first topic tackled during Tuesday night's debate between US vice presidential candidates JD Vance and Tim Walz, with both men asked if they would support Israel conducting a pre-emptive strike against Iran.

The debate, the first and only time Americans will see the two men face off before the November 5 election, took place hours after Iran unleashed a barrage of ballistic missiles against Israel that the US helped to defend against.

Democrat Mr Walz, who is Vice President Kamala Harris's running mate, said Israel's ability to defend itself is “absolutely fundamental”, and called for the hostages to be returned and an end to the humanitarian crisis in Gaza.

He then sought to portray former president Donald Trump as too unstable to be trusted at a time of crisis in the Middle East.

“Iran is closer to a nuclear weapon because of Donald Trump's fickle leadership,” said Mr Walz as he criticised Mr Trump for abandoning the Iran nuclear deal in 2018.

US vice presidential candidates show support for Israel after Iranian missile attack

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Republican Mr Vance, who is Mr Trump's running mate, said his boss had “delivered stability in the world” and said Israel should be supported to take whatever action needed “to keep their country safe”.

“We should support our allies wherever they are when they're fighting the bad guys,” Mr Vance said.

Mr Walz, 60, the liberal governor of Minnesota and a former high schoolteacher, and Mr Vance, 40, a bestselling author and conservative firebrand US senator from Ohio, have portrayed themselves as two sons of America's Midwestern heartland with deeply opposing views on the issues gripping the country.

Many had been expecting fireworks between Mr Vance and Mr Walz – who has repeatedly called his rival “weird” – but instead Tuesday's nearly two-hour debate hearkened back to a more civil time in American politics, with both men treating each other respectfully and even agreeing on some policy points.

In one exchange, Mr Walz said his teenage son had witnessed a shooting at a community centre, prompting Mr Vance to express empathy.

“I’m sorry about that. Christ have mercy,” Mr Vance said.

“I appreciate that,” Mr Walz responded.

Historically, vice presidential debates have done little to move the needle in terms of the trajectory of the presidential race. Neither Mr Vance and Mr Walz did anything to upset their respective running mates and their lengthy responses didn't create many memorable moments.

Aside from the Middle East, the two candidates were grilled on immigration, the economy, climate change, abortion rights and other issues including the state of America's democracy.

Mr Walz said that the January 6, 2021, Capitol insurrection and Mr Trump's election denial were the biggest threats to democracy.

“I think you've got a really clear choice on this election, who's going to honour democracy and who's going to honour Donald Trump,” he said.

Mr Vance meanwhile said censorship is the greatest threat to democracy.

On immigration, Mr Walz said the border crisis can only be addressed through Congress and not through the executive branch.

“We all want to solve it,” he said. “That's why we had the fairest and the toughest bill” on immigration.

Democrats and Republicans worked on this piece of legislation, he added, but as soon as it was getting ready to pass “Donald Trump said no, told them to vote against it because it gives him a campaign issue”.

On gun violence, Mr Vance blamed illegal guns being brought over the border, a mental health crisis and called for strengthening security in schools.

Mr Walz, a gun owner, responded: “Sometimes, it's just the guns.”

Despite Vance's having written Hillbilly Elegy, a popular 2016 memoir, US voters have a negative view of him, Reuters/Ipsos polling shows, with 51 per cent of registered voters saying they view him unfavourably, compared with 39 per cent who view him favourably.

Meanwhile Mr Walz was viewed favourably by 44 per cent of registered voters, with 43 per cent reporting an unfavourable view in the September 20-23 poll.