The upper chamber is known as the Senate and was originally intended to be a regulatory group providing checks and balances for the work of the Representatives – but it has been the dominant body since the mid 19th Century.

There are fewer members of the Senate – just 100 – with each state having two senators, regardless of its size.

Senators are directly elected and serve six-year terms – there are no term limits in place and many serve for several decades. The longest serving US senator was Democrat Robert Byrd who represented West Virginia for 51 years before dying in office in 2010.

The US vice-president takes a leading role in the Senate, acting as the chamber’s president. The Senate has the power to approve or block any new laws, to debate and confirm any presidential appointments to high-ranking office (as appropriate) and also to conduct investigatory trials against the president in a process known as impeachment.