New York, New York - Vice presidential candidates JD Vance and Tim Walz faced off in a surprisingly civil debate Tuesday, despite tense moments on the hot topics of migration, abortion, and the threat of war in the Middle East.

Republican Vance and Democrat Walz dug into policy and avoided the bitter personal attacks that presidential candidates Donald Trump and Kamala Harris exchanged during an often heated clash in September.

But the shadow of their bosses hung over the CBS debate, with Walz attacking Trump as a threat to democracy and unfit to lead America on the world stage, and Vance slamming Harris's record on the economy and migration as part of President Joe Biden's administration.

A key moment came near the end, when Vance refused to say whether he backed Trump's false claims to have won the 2020 election against Biden.

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Minnesota governor Walz accused him of a "damning non-answer" and blasted Trump over the January 6, 2021 attacks on the Capitol by Trump supporters.

There was also a fiery moment when Vance had his microphone briefly muted when the moderators tried to fact-check him on migration.

Walz said false and racist stories spread by Vance and Trump about migrants in the town of Springfield, Ohio "dehumanize and villainize other human beings."

He repeated Harris' pledge to sign into law "the fairest and the toughest bill on immigration that this nation has ever seen," referring to stalled bipartisan legislation that would introduce draconian measures against migrants.

Another tough exchange was over abortion, a key issue since a Supreme Court packed with judges picked by Trump overturned the national right to abortion in 2022.

Vance accused Democrats of taking a "very radical pro-abortion stance" who backed what he called "barbaric" laws that he frequently misrepresented. Walz hit back, saying he was "pro-women."

But the debate, which is likely to be the last before the November 5 vote, featured a mostly respectful tone despite the deep ideological differences between the two men.

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Vance and Walz, who both claim folksy roots in the US Midwest, said several times that they agreed with each other during the debate, and shook hands at the beginning and the end.

The usually cheerful Walz had a nervy start and stumbled several times, but became more confident, while Vance gave a smooth performance.

Most of the attacks were instead on their opposite running mates.

Trump came up again as the VP rivals took on the crisis in the Middle East after Iran's missile attack on Israel.

Walz slammed Trump's foreign policy record, accusing the ex-president of a "turn towards" Russia's Vladimir Putin and his withdrawal of the US from the 2015 Iran nuclear deal.

"As much as Governor Walz just accused Donald Trump of being an agent of chaos, Donald Trump actually delivered stability in the world," Vance countered.

Trump praised his protégé after the debate, saying on his Truth Social platform: "GREAT JOB JD – We will MAKE AMERICA GREAT AGAIN!"