It’s the running mates’ turn to battle on stage

When Republican Mike Pence goes on stage on Tuesday against Democrat Tim Kaine in their vice-presidential debate, is he likely to defend his presidential nominee Donald Trump as a "genius" for ducking income tax, as have so many campaign surrogates?

Probably, if that's the party line. But something inside him may cringe.

Pence has already released his tax returns, which Trump continues to stall despite mounting pressure, exacerbated recently by a report that he may have paid nothing for years.

In more ways than one, both VP nominees are very different from their respective running mates. Pence is sober, measured in his remarks, on the script and, to his fans, principled — unlike the flashy, free-wheeling, blustery, flip-flopping Trump.

Kaine comes across as folksy, spontaneous and trustworthy, where Clinton has been called scripted, robotic and generally untrustworthy — she and Trump have been polling record high numbers in unfavourability match-ups.

That's probably why they were picked.

But they will not get to talk about themselves, though it will be their only chance together on national stage, as much as about their running mates. Vice-presidential nominees, or their debate, don't determine the outcome.

Pence and Kaine will be closely scrutinised for their defence of their running mates and how they explain differences and disagreements. Pence will almost certainly be asked about Trump’s refusal to release his tax returns and Kaine will be probed on Clinton’s emails.