Is this too old for the job? Joe Biden claims that having lived a long life is an advantage for a president — and Donald Trump is in no position to contradict him.
78 or 81: the age of America’s next leader
Record breakers: Joe Biden and Donald Trump are already the USA's oldest presidents. Glossary
White House - The official residence of the US president, in Washington DC. Burnt by British troops in 1814, it was rebuilt and painted white to hide the smoke stains.
Neuroscientists - A scientist who studies the brain and the nervous system.
Winston Churchill - The British prime minister during World War Two, and later from 1951 to 1955.
Mahatma Gandhi - An Indian political activist and lawyer (1869-1948), who emphasised passive resistance.
Supreme Court - The highest court within the hierarchy of courts in most legal jurisdictions.
Federal - In the USA laws are made both by individual states and the federal government, which governs all states together.
Constitution - A document that sets out the fundamental rules according to which a country is governed, which are usually difficult to change.