When Joe Biden delivers his inaugural address tomorrow, the shadow of what Abraham Lincoln called the "mobocratic spirit" will cast a heavy pall over the day's usual pomp and circumstance.

On January 6, insurrectionists stormed the US Capitol, attempting to obstruct Congress's certification of Biden's victory in the electoral college. Incited by President Donald Trump promulgating a parade of falsehoods about a stolen election, and enabled by scores of Republicans who parroted them, the mob besieged a sacred attribute of constitutional democracy: the validation of the peaceful transfer of power.

The attempted insurrection was the climactic act in a five-year drama of Trumpian populism. Today, our republic confronts a spiritual disunion inspired by Trump's obstinate demagoguery and the Republican Party's toleration of his damaging rhetoric and deceitful actions.

Trump rose to political prominence in 2015 by appealing to the passions of an electorate that considered itself marginalised by cultural elites, aloof politicians and ever-diversifying national demographics. Many believed that their voices had been silenced, that powerful institutions had been arrayed against them, that they lived one election removed from the collapse of civilisation. The sense of existential crisis beckoned a guardian unconstrained by the checks of constitutional democracy.

The Capitol insurrectionists displayed a long-festering trait of Trumpism: solitary devotion to a president who claimed to shield his beleaguered constituency from this seemingly crooked political order. Trump cast himself as an outsider who could confront a system rife with fraud and deception, a leader who could seemingly lose re-election only through a complex, co-ordinated conspiracy, one that warranted drastic action. But fealty to this conception of Trump came at the expense of loyalty to the union's civic compact of ordered liberty, placing the very core of Americanism at risk.

Alexander Hamilton, one of the nation's founders, foresaw Trump's brand of populist demagoguery. In 1787, Hamilton remarked in Federalist No 1, "it seems to have been reserved to the people of this country, by their conduct and example, to decide the important question, whether societies of men are really capable or not of establishing good government from reflection and choice".

Sceptical of humanity’s innate virtue, Hamilton warned that an enduring union of constitutional checks and democratic restraint was hardly inevitable. "History will teach us," Hamilton reflected, that "the introduction of despotism . . . overturned the liberties of republics" when ambitious cynics "have begun their career by paying an obsequious court to the people; commencing demagogues, and ending tyrants".

Hamilton explained that the person who held the office of president possessed an unmatched ability to foment political disunity. A strongman who defended one constituency from another, who used the office for personal enrichment and who sowed distrust in the republic itself, would embody a demagogue's "talents for low intrigue, and the little arts of popularity", Hamilton opined in Federalist 68 (1788).

Constitutionally prescribed elections were a crucial check on this behaviour. They functioned as public hearings to ensure a candidate’s “moral” fitness for executive office. But if the voters failed to screen candidates properly, the entire experiment in self-government could collapse.

The stakes were so high because, as Hamilton wrote in Federalist 70 (1788) the executive needed “energy” — power — to secure “liberty against the enterprises and assaults of ambition, of faction, and of anarchy”. But that power necessarily meant that if he rejected popular institutions and constitutional procedures to serve his own political ambition, it could splinter Americans, giving rise to “ambitious individuals who aspired to tyranny, and the seditions of whole classes of community whose conduct threatened the existence of all government”.

Hamilton previewed what Abraham Lincoln later described as the “mobocratic spirit”. In his famous 1838 Lyceum Address, Lincoln explored how vigilantism frayed “the strongest bulwark of any Government, and particularly of those constituted like ours . . . effectually [breaking] down and destroy[ing] . . . the attachment of the People”. Lincoln warned that trading the rule of law for extralegal mob justice would sever mediating institutions from their democratic obligation to order liberty and restrain popular passions. Mobocracies sustained themselves on an authoritarian rejection of law, reason and constitutional constraints. A once free society then mutated into a repressive demagogic regime.

Lincoln, too, saw a virtuous president as an essential bulwark against mobocracies. The chief executive must rise above sectarian division, never using the office to consolidate one's prejudiced motives at the expense of constitutional duties. The American president served temporarily as “the representative man of the nation, united by a purpose to perpetuate the union and liberties of the people”, Lincoln outlined one month before his 1861 inauguration.

For Lincoln, virtuous democracy charged representatives to restrain and channel the passions of their constituents, neutering the innate human tendency to mob action. A popular leader possessed unusual power to shape "public sentiment" — the key to the success or failure of any initiative — mould political narratives and harness a devoted following.

Representative democracy thus mandated dispassion, honesty, restraint and subordination to the Constitution. Self-government, Lincoln instructed, depended on the people's "acquiescence" to the provisions of popular elections. Devotion to the rule of law secured the common good. As long as elected representatives “continue to execute all the express provisions of our National Constitution”, Lincoln explained in his first inaugural address in 1861, "the union will endure for ever, it being impossible to destroy it except by some action not provided for in the instrument itself“.

Such illicit actions included mob rule. When a political minority unduly obstructed the constitutional process or rejected the outcome of a legitimate election, it courted disunion. "The rule of a minority, as a permanent arrangement, is wholly inadmissible; so that, rejecting the majority principle, anarchy or despotism in some form is all that is left," Lincoln explained amid the shadow of southern states seceding from the union before his 1861 inauguration.

Happily, the genius of the American system absolved political minorities from resorting to mob violence to protect themselves from the majority, Lincoln believed. The Constitution sheltered individual liberties and would check the power of the majority. “A majority held in restraint by constitutional checks and limitations, and always changing easily with deliberate changes of popular opinions and sentiments, is the only true sovereign of a free people,” he concluded.

Hamilton and Lincoln lived during eras in which Americans regarded their republic as a unique experiment in political liberty within a repressive, monarchical world. And yet, both argued that the very attribute of "American exceptionalism" posed the greatest danger to the republic's fate: namely, the vulnerability of self-government. Both men feared demagogues who might corrupt the body politic and turn a free citizenry against the democratic institutions that safeguarded their liberty.

A demagogue who planted doubts about the stability of the democratic system could provoke the free citizenry to weaken their own constitutional order. For most of American history, such figures have largely stayed out of the executive office, thanks in part to a strong party system and leaders who safeguarded our mores and government by law, not whim.

But Trump has upended these customs. He has stoked just the "mobocratic spirit" that scared Hamilton and Lincoln. In commanding allegiance to his cult of personality, Trump's reckless duplicity has licensed a minority to defy the constitutional structure. He inspires an insurrectionary mood that functions outside the rule of law and beyond the boundaries of Union.

Through demagogic appeals to personal fidelity, Trump has energised an insurrectionary "public sentiment" within a swath of the electorate. Even when Congress reconvened after the attempted Capitol insurrection, 127 Republican lawmakers objected to certifying the electoral college results. Even more whopping: a new NPR/PBS/Marist poll found that 86 per cent of Republicans believe the election results are not accurate.

Only time will tell whether we repudiate today's spirit of disunion to reclaim, as Lincoln said, "the better angels of our nature" and stand once more as "the last best, hope of earth“. Doing so will require strong leadership that prioritises public good over narrow passion, accepts limitations imposed by law and most importantly recommits to the peaceful transfer of power.

• Andrew F. Lang is an associate professor of history at Mississippi State University and the author of A Contest of Civilisations: Exposing the Crisis of American Exceptionalism in the Civil War Era