US voters across all 50 states were going to the polls on Tuesday to decide one of the most tightly contested presidential contests in recent history. The outcome of the race between Kamala Harris, the Democratic vice president, and Donald Trump, the former Republican president, remained a toss-up as voters cast their ballots, with 270 electoral votes needed to win. For months, the two candidates’ campaigns have focused on the seven swing states that will almost surely decide the election: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin. About 80 million US citiz…