In the run-up to the US presidential election, pundits proclaimed that the outcome would be “historic”. What they meant, invariably, was that they expected Democratic candidate Hillary Clinton to shatter precedent by becoming the country’s first woman president. Instead, Washington DC now prepares for the inauguration of president-elect Donald Trump. But the New York businessman’s victory was also historic. While both his candidacy and his impending presidency call to mind some features of the Republican party’s recent history, they also represent a significant departure from the country’s past political patterns.

Trump’s win was one of the greatest upsets in American political history. But it was far from the landslide that Trump claimed and marked only the fifth time that a presidential candidate won the electoral college while losing the popular vote. Trump also will enter the presidency with the lowest favourability ratings in modern history.

The controversies of recent weeks, from Trump’s social media battles against film stars to the sensational (and unsubstantiated) intelligence reports about his putative financial and carnal dealings with Russia, have vaporised the “honeymoon” that incoming presidents traditionally enjoy.

Trump may yet become a popular leader. George W Bush won an even closer and more contentious election in 2000, faced similar “not my president” opposition from the left and still won a second term. But Bush’s message of “compassionate conservatism” appealed to a much broader constituency than Trump’s hard-edged culture warfare and the Republican party united behind him for most of his presidency.

Trump, by contrast, won the party’s presidential nomination by staging something like a coup against its leadership. In that sense, he resembles Barry Goldwater, the rightwing Arizona senator who was the Republican presidential candidate in 1964. Like Trump, Goldwater was an anti-establishment firebrand with a habit of making extreme statements on sensitive subjects (such as race and nuclear weapons). The Republican organisation opposed his candidacy on the grounds that his conservative beliefs were too far removed from the party’s mainstream, but he seized the nomination by mobilising an army of impassioned grassroots activists.

After presiding over a divided party convention, the prickly and headstrong Goldwater refused to pivot toward a more measured, level-headed “presidential” posture. Like Trump, he had no interest in reaching out to groups that were sceptical of his candidacy, such as minorities and college graduates. He did, however, appeal to many less-educated voters in the white working class who hadn’t previously taken much interest in politics.

Indeed, Goldwater’s campaign, like Trump’s, was founded on the belief that a “hidden majority” of Americans would turn out to the polls when they finally were offered a real alternative to status-quo, business-as-usual politics. Goldwater said he represented “a choice, not an echo”. That phrase became the battle cry of his champion, Phyllis Schlafly, who, before she died in September aged 92, hailed the same populist potential in Trump.

Goldwater, unlike Trump, lost the presidential election in a wipeout and dragged down Republican congressional candidates with him. But, in 1964 as in 2016, many Republican candidates disavowed their party’s presidential nominee, or at least distanced themselves from his candidacy. For some Republicans running for the House or Senate last year, Trump’s bullying behaviour, lack of interest in the fine details of policy and government and intemperate remarks about Mexican “rapists” and “murderers” disqualified him from the presidency. Many more called for Trump to abandon the race after a 2005 hidden-mic recording of his crude sexual comments became public.

In the wake of Trump’s unexpected victory, it has suited both him and his erstwhile intraparty critics to reconcile. The Republican leadership has insisted that party members in both Congress and the White House will be singing from the same hymn sheet. Republicans have exercised control of both the legislative and executive branches for only six of the past 80 years, so they’re anxious to make the most of this opportunity.

But this Republican unity is more apparent than real. Unlike Ronald Reagan in 1980 or Barack Obama in 2008, Trump didn’t have much of a “coat-tail effect” on down-ballot candidates. Few Republicans in Congress feel they owe their elections to Trump. In fact, in many traditionally Republican suburban districts, Trump performed significantly less well than Mitt Romney did in 2012. In dozens of these districts, the Republican congressional candidates ran ahead of Trump by double digits.

More importantly, Trump and the Republican party stand for very different things. Ever since the election of Reagan in 1980, the party has been dominated by ideological conservatism. Trump is not in any meaningful sense a conservative; he is, rather, a populist.

Populism has a long and durable tradition in American politics. Much of Trump’s campaign rhetoric unconsciously echoes the 1892 platform of the People’s party (better known as the Populists), from its denunciations of biased media and “imported pauperised labour” to its insistence that the nation had been “brought to the verge of moral, political and material ruin”.

Populism is in many ways an appealing doctrine. Trump won the presidency because he sensed, as no other candidate did, that many of the “plain people” (to borrow another phrase from the Populists’ 1892 platform) feel ignored and even despised by the elites of both parties. His candidacy, like that of Vermont senator Bernie Sanders on the left, resonated because increasing numbers of citizens believe that the economic and political systems of the country are rigged against them. Trump has complicated the traditional calculus of left and right in interesting ways, winning over many union members who feel threatened by free trade and globalisation.

Most successful American presidents, from Franklin D Roosevelt to Reagan to Bill Clinton, have been populists to some extent. But leaders of both parties also have been wary of populism’s tendency to slide into demagoguery. History has shown that populists find it difficult to resist scapegoating minorities and outsiders, proffering simplistic and unrealistic solutions for complicated problems and destroying trust in every social or government institution other than the military and police.

Trump in many ways resembles previous populists who ran for the presidency, such as Patrick Buchanan (who also campaigned on the slogan “America First”) and Alabama governor George Wallace. But there has never been a full-blooded populist in the White House, with the arguable exception of Andrew Jackson.

Trump’s populism conflicts at many points with the beliefs most Republicans have supported for the past century. His call for a trillion-dollar upgrade to the nation’s infrastructure suggests an affinity with Dwight Eisenhower’s construction of the national highway system, but Trump doesn’t appear to share Ike’s budget-balancing fiscal conservatism or his internationalism. His indifference to hot-button social issues such as gay marriage puts him at odds with religious conservatives. His willingness to spend federal funds in pursuit of American greatness, as, for example, by building a wall on the Mexican border, offends minimal-government libertarians. His divisive rhetoric undermines a half century of effort by Republican activists to build a broader and more inclusive party.

Trump’s populism makes him an outsider in the party that he nominally leads. So, too, does the fact that he is the first president in US history to enter office without political or military experience. But Trump’s distance from traditional politics raises hopes that he may be able to break through some of the nation’s seemingly intractable problems.

For example, both Republicans and Democrats agree that the country’s corporate and individual tax systems are a mess. Genuine reform, of the sort Reagan and Congress achieved in 1986, can happen if Trump shows a willingness to stand up against special interests and forge bipartisan coalitions.

The American dream of socioeconomic advance from generation to generation depends on a growing economy. That dream can’t be fulfilled if economic growth creeps along at the anaemic pace of the past decade and working-age men continue to have a lower labour participation rate than they did in 1940. Neither of America’s political parties has seriously focused on increasing employment, but already this is becoming a greater priority for both Republicans and Democrats thanks to Trump.

Future historians may see the Republicans under Trump as a return to the party’s now-forgotten traditions of the pre-conservative era, from the 1860s to the 1920s. In those days, when the party saw itself as the champion of the white working class, it was distinguished by protectionism, anti-internationalism, acceptance of powerful government and an emphasis on social order over individual freedom, all elements that some day may be known as Trumpism.

The president-elect, who made much of his money from casinos, represents a huge, historic gamble for both the Republican party and the country. Whether he succeeds or fails, he is likely to reshape America’s political system in far-reaching ways.