from Daily Mail:

• When voters cast a ballot for president, they are actually choosing members of the Electoral College – who then choose the president
• 30 states have laws saying the electors must vote in line with the popular vote in that state but the rest do not 
• In 2016 group of ‘Hamilton electors’ tried to vote for a unity candidate to stop Trump getting into power and became ‘faithless electors’
• In Colorado Micheal Baca wrote in John Kasich but was removed; he went to court and has a federal appeals court ruling that he was allowed to vote freely
• But in Washington, the State Supreme Court said electors could be fined for not following the popular vote
• Now Supreme Court will decide, with potential to cause chaos if 2020 election is knife-edge close and electors become ‘faithless’