Donald Trump's campaign is suing Nevada officials over how early voting there was carried out.
The dispute revolves around the fact that early voters found that polling stations were left open for hours after they were scheduled to close. That appears to have happened because of the huge interest in casting ballots early – in particular from Latino voters – which meant that queues extended for hours even after the scheduled close.
If successful, the lawsuit would see early votes set aside if Nevada is close. That could mean that thousands of votes would be left out of the count and so could easily swing the election.
The suit is thought to be one of a number that could be filed by the Republicans or Donald Trump if they seek to challenge how the election has been conducted.
Under election law, anyone who is in the queue to vote must be able to cast their ballot, even if that happens after the scheduled close.
Nevada's Republican chair, Michael McDonald, decried the fact that polling places had been left open in Clark County so that voters could get a chance to vote.
"Last night, in Clark County, they kept a poll open until 10 o'clock at night so a certain group could vote," Mr McDonald said at a Sunday rally for Trump. "The polls are supposed to cose at seven. This was kept open until 10. Yeah, you feel free right now? You think this is a free and easy election? That's why it's important."
KTNV political analyst Jon Ralston has said that the huge interest from hispanic voters has probably meant that Donald Trump has lost that state.
Claims of rigging or other problem voters have blighted the election process this year, with claims of voter suppression being made by both sides.
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