North Carolina: With a slew of new polls tilting in Hillary Clinton's favour, her campaign has begun operating in states considered absolutely unwinnable to the Democratic Party in normal circumstances.

The campaign has spent $US2 million on advertising in the Republican stronghold of Texas this week. No strategists seriously believe Mrs Clinton can win the state, and observers are divided over whether the campaign is seeking to simply unsettle the embattled Trump campaign with its confidence or lay the groundwork for Democratic gains in the state in the coming years.

It has long been a dream of Democrats to take the vast state from Republicans, effectively putting the White House out of reach of the GOP.

The Clinton machine is also spending money in the deeply conservative state of Arizona, a state where Mr Trump has made much out of his alliance with the hard-line anti-immigrant elected sheriff, Joe Arpaio, who championed the so-called "birther movement" with the candidate. The campaign has dispatched some of its most powerful spokespeople to campaign in the in the state, including Michelle Obama, Chelsea Clinton and Bernie Sanders.