President Donald Trump made his final effort to overturn the 2020 election yesterday, as his allies challenge the electoral college count in Congress. His earlier efforts failed when the Supreme Court rejected Texas's lawsuit to throw out the results in four swing states. Afterward, Texas Republican Party chairman Allen West declared that "law-abiding states should bond together and form a union of states that will abide by the Constitution" — a seeming endorsement of secession.

As we say goodbye to the sorest loser in presidential history, a man making unprecedented attempts to undermine the will of the people, we should remember a candidate who took a very different attitude towards defeat. Not only did he accept his loss, he spent the final days of his campaign barnstorming the country to build support for his opponent's impending victory, setting aside his long-held desire for the presidency for the higher principle of national unity.

The candidate was Stephen A. Douglas, the Democratic senator from Illinois, who realised a month before the 1860 presidential election that he was going to lose to Abraham Lincoln.

That October, Republicans swept statewide elections in Ohio, Indiana and Pennsylvania — three swing states Lincoln needed to win the presidency. Elections for state offices were held separately from the election for president.

Douglas had sought the presidency in three straight elections, and it must have galled him to lose the prize to Lincoln, of all people. The two had been rivals for more than 20 years, since the days when they had argued politics around the stove in the back room of Joshua Speed’s store in Springfield, Illinois. Throughout those years, Douglas's achievements had surpassed those of Lincoln. Elected to the Senate at age 33, the 5ft 4in Douglas was known nationwide as "the Little Giant" — builder of railroads and celebrated orator. "Time was I was in his way some," an envious Lincoln lamented in a letter, "but he had outgrown me, and [be]strides the world; & such small men as I am, can hardly be considered worthy of his notice."

In 1858, Douglas defeated Lincoln in a race for a US Senate seat in Illinois. The Douglas-Lincoln contest was seen as a proxy for the nationwide debate on slavery. "The battle of the Union is to be fought in Illinois," opined the Washington States. Lincoln insisted that the Declaration of Independence granted Blacks as well as Whites the right to profit from their labour. That was one of Lincoln's "monstrous revolutionary doctrines," argued Douglas, who believed that the Declaration applied only to Whites, and warned that "Negro equality" would ultimately lead to miscegenation. Lincoln wanted to ban slavery from the territories. Douglas had staked his political career on the doctrine of popular sovereignty, which granted settlers the right to establish free or enslaved territories.

At the outset of the campaign, Douglas accused his opponent of fomenting a civil war by insisting that the nation could not endure "half-slave and half-free".

"Mr Lincoln advocates boldly and clearly a war of the North against the South, to be continued relentlessly until one or the other shall be subdued, and all the states shall either become free or become slave," he declared during a speech from the balcony of Tremont House in Chicago.

Douglas, though, was a practical man, who understood that there are no permanent friends or enemies in politics, only permanent interests. Since shepherding the Compromise of 1850 through Congress, he had seen himself as a defender of the Union, occupying a moderate position between Northern abolitionists and Southern fire eaters who threatened to break up the country over the issue of slavery. While Douglas himself had radicalised both extremes by pushing the Kansas-Nebraska Act through Congress, he still firmly believed that the Constitution prohibited secession. As a champion of Manifest Destiny, he also considered a strong union essential to his vision of a coast-to-coast nation, knit together by a network of railroads converging on his home town of Chicago.

In the 1860 election, once the Republican victory was assured, Douglas saw only one way to hold the country together: persuade the Southern states to accept Lincoln as their president. Douglas had once told a campaign audience that Lincoln's ascension to the nation's highest office would be "a great public calamity". As Election Day approached, though, Douglas stopped campaigning for himself, and started campaigning against secession.

"Mr Lincoln is the next president," Douglas told his secretary. "We must try to save the Union. I will go south."

Republicans did not take the threat of secession seriously. Douglas did. He was more familiar with the South than most Northerners. His first wife was from North Carolina. She received a Mississippi plantation as a wedding gift. After she died, its stewardship passed to Douglas. He believed — wrongly, as it turned out — that his fame and rhetorical skills could stir Unionist sentiment among sensible Southerners, despite calls for secession from their newspapers and their intemperate politicians.

With his candidacy doomed, Douglas carried his anti-secession message through the heart of Dixie: Memphis, Nashville, Chattanooga in Tennessee; and Atlanta and Macon, in Georgia. In Kingston, Georgia, according to his biographer, Robert W. Johannsen, Douglas "denied that the Constitution conferred on any state the right to secede and declared that if a state should secede the Chief Executive was obligated to resist it".

Four days before the election, Douglas spoke from the steps of the Alabama State House in Montgomery — a future Confederate capital. He did not want Lincoln to win, Douglas told the crowd, but "if Lincoln is elected, he must be inaugurated“. Obeying the results of a fair vote was a principle that held the country together: "I hold that the election of any man on Earth by the American people, according to the Constitution, is no justification for breaking up this government."

Douglas finished fourth out of four candidates in the electoral college, carrying only Missouri. (Lincoln was the candidate of the North, John Breckinridge of the Deep South and John Bell of the Border States. The electorate was polarised over slavery. Douglas did not believe slavery was worth fighting over, one way or another, and so he had no strong regional base.) Lincoln won 39 per cent of the popular vote — none at all in the Southern states, where he wasn't on the ballot — but Douglas saw no rationale for questioning his legitimacy, since he had carried a majority of the electoral college.

Although he had every reason to resent Lincoln, Douglas turned out to be one of the most gracious losers in presidential history. Not only did he attend the inauguration, but when Lincoln could find no place to lay his stovepipe hat as he stood to address the crowd, Douglas stepped forward, said "Permit me, sir" and held the topper in his lap throughout the new president's 30-minute speech.

"I've known Mr Lincoln a longer time than you have, or than the country has," Douglas told a friend. "He will come out all right, and we will all stand by him."

Douglas spent the Secession Winter of 1860-61 trying to negotiate a compromise that would restore the Union. The Senate passed a constitutional amendment protecting slavery in the states where it existed — a measure not even Lincoln opposed. It wasn't enough for the South.

Once the newly formed Confederate States of America bombed Fort Sumter, and reasoning with the secessionists was no longer possible, Douglas staunchly supported Lincoln's war effort — a position not shared by all Democrats, especially those in the border states. He met with Lincoln at the White House to discuss raising an army. Lincoln wanted 75,000 men to put down the rebellion. Douglas, better acquainted with the Southern aristocracy's warrior ethic, suggested 200,000.

"You do not know the dishonest motives of these men as well as I do," he told Lincoln.

Hearing rumours that pro-Southern elements in his own state were threatening to join the Confederacy, Douglas returned home to deliver what would become known as his "Protect the Flag" speech at the State House in Springfield. As the leader of the Northern Democrats, he sought to unite his party behind Lincoln's leadership. In wartime, he believed, patriots supported the president, whether they'd voted for him.

"Do not allow the mortification, growing out of defeat in a partisan struggle, and the elevation of a party to power that we firmly believed to be dangerous to the country - do not let that convert you from patriots into traitors to your native land," Douglas urged his fellow Democrats. "The greater the unanimity the less blood will be shed."

Six weeks later, worn down by the presidential campaign and his subsequent struggles against secession, the 48-year-old Douglas died of typhoid fever in Tremont House, the same Chicago hotel where he had begun his Senate campaign against Lincoln. Mourning the loss of a loyal opponent, Lincoln ordered the White House and all department buildings draped in black.

History remembers Lincoln and Douglas as antagonists, but they ended their relationship as allies against the greatest threat their country had faced, bonded, finally, by their shared belief in the Union.

• Edward McClelland is a journalist, historian and author of Midnight in Vehicle City: General Motors, Flint, and the Strike that Created the Middle Class. This opinion was written hours before thousands of Donald Trump supporters stormed the Capitol