There's belief Republican candidate JD Vance completely lost credibility as today's vice-presidential debate ended. 

The contest against Democrat Tim Walz was mostly civil and policy focused. 

But Vance dodged a question on Donald Trump challenging the 2020 election results - saying he's 'future-focused'. 

Former US ambassador to New Zealand, Mark Gilbert, says until that moment, Vance had restored likeability and seemed strong.

"It was a very awkward moment - and if I was sitting there as an undecided voter, I would have really recoiled at the answer he gave about 2020."

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