US elections key dates: When are the 2018 midterms and the 2020 presidential campaign?

Elections to the US Senate and the House of Representatives take place this November

Donald Trump and his Republican party will face their first real electoral challenge since becoming US president this November when voters go to the polls in the midterm elections.

The Democrats have a chance to win back the House of Representatives from its current Republican majority, and perhaps the Senate also.

These midterms are already set to be the most expensive ever, with advertising passing $1bn, and they are also marked by a surge of female candidates, with 40,000 women expressing an interest in running.

A shift in power could radically change Trump's ability to push his agenda through both houses, such as the situation was for President Obama after Republican victories in the 2014 midterms.

A number of key dates will be crucial bell weathers for gauging the level of support Trump maintains across the US this November, and into 2019 as prospective candidates will emerge to challenge the president in 2020.

August and September 2018: Primaries

Various states will hold primaries to select candidates for the midterm elections across August and September. This includes Hawaii, Vermont, Minnesota and Wisconsin.

6 November 2018: Midterm elections

There will be elections for governorships of 36 states and three US territories, as well as for Mayor of the District of Columbia. Most state legislative chambers are holding regularly scheduled elections also.

Several major cities will hold mayoral elections, including San Francisco, Phoenix and Washington DC.

January 2020: Primaries and caucuses begin

The traditional primaries and caucuses will begin in Iowa and New Hampshire, as states decide upon candidates for both the Democratic and Republican nomination for the presidency.

Super Tuesday will occur in early March, when a several states decide on one day, often pushing the respective winners to the fore. However, the contest can run on until the final primaries in June, and even to the conventions across the summer, if there is a deadlock.

Summer 2020: Conventions

The Democrats will hold their convention between 13-16 July, in Houston, Miami Beach or Milwaukee, and decide upon their candidate for the presidency.

Because they currently hold the White House, the Republicans will hold their convention after the Democrats, although they have not yet fixed a date. It will be held in the city of Charlotte, North Carolina.

Unless some major internal party conflict emerges, it is likely this convention will support President Trump to contest the presidency for a second term.

3 November 2020: Presidential election

US voters will go to the polls to decide between re-electing Donald Trump for a second term, or choosing whoever emerges as his Democratic opponent.

The election will be held at the same time as elections to the Senate and the House of Representatives.