An epic showdown is expected at tomorrow's presidential debate between Kamala Harris and Donald Trump.

The VP and former President are facing off in the battleground state of Pennsylvania.

Millions are expected to tune into the ABC-broadcast clash - which has no live audience, with microphones muted when candidates aren't explicitly in speaking time.

Former US debate moderator Dominic Carter says it's the pair's first face-to-face moment.

"Trump - he's done many presidential debates. It's the first time for Kamala Harris, the Vice-President at the top of the ticket." 

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