Your guide to the mid-terms...
WHAT ARE THE US MID-TERMS?
US voters deliver their verdict on Donald Trump’s first two years in the White House.
All 435 seats in the House of Representatives are up for grabs and 35 of the 100-strong Senate.
Elections are also taking place for 36 of the 50 state governor posts.
The House of Representatives at present has 235 Republicans and 193 Democrats with seven seats vacant. The Senate has 51 Republicans and 49 Democrats.
WHY DO THEY MATTER?
Control of Congress – the House and the Senate – will determine America’s path over the next few years. Congress is the main check
on the president’s authority. In control the Democrats could block appointments by Mr Trump, vote down his laws and start impeachment proceedings against him.
His opponents fear that if the Republicans retain control it will embolden an already authoritarian president. The first casualty could be the Attorney General Jeff Sessions who appointed Robert Mueller, above, to investigate Russian meddling in the 2016 presidential elections and alleged collusion with the Trump team.
Trump may even sack Mueller if he wins big tonight.
WHAT’S LIKELY TO HAPPEN?
Polls have the Democrats set to win the House with the Senate race too close to call.
More cautious voices play down Democrat chances and note the polls have been wrong before, most noticeably in 2016 when the majority called for Hillary Clinton.
Although winning the Senate looks easier on paper, of the 35 seats in play, the Republicans defend nine and the Democrats 26.
COULD TRUMP PULL OFF ANOTHER SURPRISE?
Mr Trump has a good story to tell on a growing economy and can also claim to have delivered on his promises to cut taxes.
The Democrats have gained support among college-educated and female voters disgusted by the president’s attitude to women.
WHAT COULD BE THE FALL-OUT?
Trump’s 40% approval rating is one of the lowest recorded and he is still extremely divisive, but Clinton and Obama both suffered big mid-term losses and were re-elected.
If the Democrats fall short it would provoke much soul searching over whether to turn to the left.