Mr Vance, 40, and Mr Walz, 60, each claim to be the true voice of the crucial Midwestern swing states – including Michigan and Wisconsin – that could decide an election that remains on a knife-edge with five weeks to go.
Both have been out of the spotlight as of late, but Mr Walz offered a brief message on X: “Looking forward to tonight.”
History suggests vice-presidential debates rarely move the dial much. But in an election campaign that has seen Harris step in for US President Joe Biden unprecedentedly late in the game, the contest on Oct 1 may have added significance.
The race has seen Mr Vance and Trump use increasingly divisive rhetoric and even falsely accuse immigrants of eating people’s pets – meaning the debate is almost guaranteed to make for fiery television.
“It will whet a lot of people’s appetites for November 5,” Mr Thomas Whalen, an associate professor of social sciences at Boston University, told AFP.
But the debate itself risked being overshadowed by Mideast tensions, after Iran launched ballistic missiles against Israel, which said it largely repelled the attack.
Trump, visiting swing state Wisconsin on Oct 1, made zero mention of Mr Vance or the V-P debate in a rambling address. But he did insist that “if I were in charge, today’s attack on Israel never would have happened.”
Should Ms Harris and Mr Walz win, he warned, “the world goes up in smoke.”
Ms Harris for her part pledged her “unwavering” commitment to the security of Israel after Iran launched what she called “a reckless and brazen attack” on America’s ally.
She said she “fully” supported Mr Biden’s order for the US military to shoot down some of the missiles.
The CBS clash also comes as several states dig out from enormous storm Helene, which has left at least 130 people dead and brought misery to thousands more.
The devastation, and how to address such disasters, is likely to come up during the debate.
Watch: Vance, Walz set for US V-P debate clash
