US voters on Tuesday will elect a president and vice president, 87% of Congress members, 11 of 50 state governors, and thousands of state and local officials and judges nationwide.

Global attention is focused on the presidential race with Vice President Kamala Harris, 59, a Democrat, facing former President Donald Trump, 78, a Republican, who left office in January 2021 after serving four turbulent years. If elected, he could not serve a third term.

Polls, notoriously inaccurate in the last two presidential elections, show Trump and Harris in a statistical deal heat.

They also indicate Democrats have a chance to regain control of the House of Representatives, while Republicans are likely to win a majority in the Senate.

A potential “trifecta” Republican win with Trump in the White House and his party assuming control of Congress could have far-reaching consequences for climate, energy, and related trade policies, and US diplomacy with friend and foe alike, particularly in Asia and Europe.

The US uses an electoral college to indirectly elect a president, which can create a scenario where a candidate may obtain the most popular vote and still lose the election. The most recent examples are from 2000 and in 2016 when Trump obtained fewer votes than Hillary Clinton but won in the Electoral College.

This presidential contest is atypical for several reasons:

First, Harris was not elected to head the ticket as candidate by competing through state primaries, a vetting process that is the norm in both political parties. Primaries award delegates, and candidates must attain a certain number of them to win the nomination and appear on the general election ballot.

Instead, she became candidate in July when party elders pressured President Joe Biden, 81, who had won all primaries, to drop out of the race after a stumbling debate performance against Trump that reinforced public concerns over his mental fitness to remain in office. At the time, internal party polls showed Biden losing handily to Trump.

Harris’ ascension so late in the election cycle as a major party candidate for the Oval Office has no precedent in modern America. If elected, she would be the first woman to serve as president and furthest left of centre politically in generations.

Trump, in turn, is looking to regain power to serve a second, non-consecutive term, a rarity in US politics. Only Grover Cleveland who served as the nation’s 22nd and 24th presidents in 1885-89 and 1893-97 achieved the feat.

Trump, a populist who lost a close election to Biden in 2020, narrowly survived an assassination attempt at a campaign rally on 13 July while a second effort on his life in September was thwarted before shots were fired. He is the first former president convicted of a crime; his fraud judgement is under appeal.

Why Harris and Trump are a world apart on energy and climate