That case is well within living memory. But an election much further back produced even more damaging results.

The campaign of 1876 ended with the electoral college in the balance as three states were disputed. Out of deadlock, eventually, came a political deal, giving the Republican Rutherford Hayes the presidency at the expense of Samuel Tilden, who like Gore, and indeed Hillary Clinton in 2016, won the popular vote.

Tilden’s compensation was that his party, the Democrats, were allowed to put an end to Reconstruction, the process by which the victors in the civil war abolished slavery and sought to ensure the rights of black Americans, via the 13th, 14th and 15th constitutional amendments.

The awful result was Jim Crow, the system of white supremacy and segregation which lasted well into the 20th century and whose legacy remains crushingly strong in a country now gripped by protests against police brutality and for systemic reform.

Eric Foner, now retired from Columbia University, is America’s pre-eminent historian of the civil war, slavery and Reconstruction, a prize-winner many times over. He told the Guardian the US of 2020 is not prepared for what may be around the corner.

“In 1877 there were three states, Florida, South Carolina, Louisiana, where two different sets of returns were sent up, one by the Democrats, one by the Republicans, each claiming to have carried the state.

“There was no established mechanism and in fact, in the end, we went around the constitution, or beyond the constitution, or ignored the constitution. It was settled by an extralegal body called the Electoral Commission, which was established by Congress to decide who won.”

National Republican chart from 1876 featuring Rutherford Hayes for president and William Wheeler for vice-president. Photograph: Education Images/Universal History Archive/Universal Images Group/Getty Images

Through wheeling and dealing in smoky back rooms as well as the precincts of Capitol Hill, that process produced a result.

“If there is such a dispute this November,” Foner says, “one of the things that is similar to 1876 is that today you have a divided Congress. Back then, just as now, you had Republicans in control of the Senate and Democrats in control of the House. And that gave each party a lot of power.”