The Trump presidency will change American history, for better or for worse.

Two government experts share three possible scenarios for what America could look like after the Trump's presidency ends.

The first scenario is that he'd lose public support and not get reelected, be impeached, or resign, thus making his administration a fleeting moment in history books and films.

The second scenario would be that Trump and the Republicans continue to win with a white nationalist appeal, engineering a new white majority in Congress, statehouses, and the Supreme Court.

The third and more likely scenario for a post-Trump presidency world would be marked by polarization creating a democracy without solid guardrails.

The following is an excerpt from "How Democracies Die" by Steven Levitsky and Daniel Ziblatt.

Turning back to our own country, we see three possible futures for a post-Trump America. The first, and most optimistic, is a swift democratic recovery.

In this scenario, President Trump fails politically: He either loses public support and is not re-elected or, more dramatically, is impeached, or forced to resign.The implosion of Trump's presidency and the triumph of the anti-Trump resistance energize the Democrats, who then sweep back into power and reverse Trump's most egregious policies.

If President Trump were to fail badly enough, public disgust could even motivate reforms that improve the quality of our democracy, as occurred in the aftermath of Richard Nixon's resignation in 1974. Republican leaders, having paid a heavy price for their association with Trump, might end their flirtation with extremist politics. In this future, America's reputation in the world would be quickly restored. The Trump interlude would be taught in schools, recounted in films, and recited in historical works as an era of tragic mistakes where catastrophe was avoided and American democracy saved.

This is certainly the future many of us hope for. But it is unlikely.

Recall that the assault on long-standing democratic norms — and the underlying polarization driving it — began well before Donald Trump ascended to the White House. The soft guardrails of American democracy have been weakening for decades; simply removing President Trump will not miraculously restore them.

Although Trump's presidency may ultimately be seen as a momentary aberration with only modest footprints on our institutions, ending it may not be enough to restore a healthy democracy.

A second, much darker future is one in which President Trump and the Republicans continue to win with a white nationalist appeal.

Under this scenario, a pro-Trump GOP would retain the presidency, both houses of Congress, and the vast majority of statehouses, and it would eventually gain a solid majority in the Supreme Court. It would then use the techniques of constitutional hardball to manufacture durable white electoral majorities. This could be done through a combination of large-scale deportation, immigration restrictions, the purging of voter rolls, and the adoption of strict voter ID laws.

Measures to reengineer the electorate would likely be accompanied by elimination of the filibuster and other rules that protect Senate minorities, so that Republicans could impose their agenda even with narrow majorities.

These measures may appear extreme, but every one of them has been at least contemplated by the Trump administration.

Efforts to shore up the Republican Party by engineering a new white majority would, of course, be profoundly anti-democratic.

Such measures would trigger resistance from a broad range of forces, including progressives, minority groups, and much of the private sector. This resistance could lead to escalating confrontation and even violent conflict, which, in turn, could bring heightened police repression and private vigilantism — in the name of "law and order."

For a sense of how such a crackdown might be framed, watch recent NRA recruitment videos or listen to how Republican politicians talk about Black Lives Matter.

Such a nightmare scenario isn't likely, but it also isn't inconceivable.

In this June 2, 2016, file photo, a woman holds hats to get them autographed by Republican presidential candidate Donald Trump during a rally in San Jose, Calif. Trump’s “Make America Great Again” hats proudly tout they are “Made in USA.” Jae C. Hong/AP

It is difficult to find examples of societies in which shrinking ethnic majorities gave up their dominant status without a fight. In Lebanon, the demographic decline of dominant Christian groups contributed to a fifteen-year civil war. In Israel, the demographic threat created by the de facto annexation of the West Bank is pushing the country toward a political system that two of its former prime ministers have compared to apartheid.

And closer to home, in the aftermath of Reconstruction, southern Democrats responded to the threat posed by black suffrage by disenfranchising African Americans for nearly a century. Although white nationalists remain a minority within the GOP, the growing push for strict voter ID laws and the purging of voter rolls — championed by influential Republicans Attorney General Jeff Sessions and Commission on Election Integrity Co-chair Kris Kobach — suggest that electoral reengineering is on the GOP agenda.

The third, and in our view, most likely, post-Trump future is one marked by polarization, more departures from unwritten political conventions, and increasing institutional warfare — in other words, democracy without solid guardrails.

President Trump and Trumpism may well fail in this scenario, but that failure would do little to narrow the divide between parties or reverse the decline in mutual toleration and forbearance. To see what politics without guardrails might look like in the United States, consider North Carolina today. North Carolina is a classic "purple" state.

With a diversified economy and an internationally recognized university system, it is wealthier, more urban, and better educated than most southern states. It is also demographically diverse, with African Americans, Asian Americans, and Latinos making up about a third of the population. All this makes North Carolina more hospitable terrain for Democrats than are the states of the Deep South.

North Carolina's electorate resembles the national one: It is evenly split between Democrats and Republicans, with Democrats dominant in such urban centers as Charlotte and Raleigh-Durham and Republicans dominant in rural areas. The state has become, in the words of Duke law professor Jedediah Purdy, a "microcosm of the country's hyper-partisan politics and growing mutual mistrust."

Museum manager Jeff Bell adheres informative backing to gender-neutral signs in the 21C Museum Hotel public restrooms on May 10, 2016, in Durham, North Carolina. Sara D. Davis/Getty Images

Over the last decade, partisans have battled over Republican-imposed abortion restrictions, the Republican governor's refusal of Medicaid as part of the Affordable Care Act, a proposed constitutional amendment to ban same-sex marriage, and, most famous, the 2016 Public Facilities Privacy & Security Act (the "Bathroom Bill"), which barred local governments from allowing transgender people to use public bathrooms for the sex they identify as.

All these initiatives triggered intense opposition. As one veteran Republican put it, state politics has become "more polarized and more acrimonious than I've ever seen it. . . . And I worked for Jesse Helms."

By most accounts, North Carolina's descent into all-out political warfare began after the Republicans won control of the state legislature in 2010. The following year, the legislature approved a redistricting plan that was widely viewed as "racially gerrymandered" — districts were carved out in ways that concentrated African American voters into a small number of districts, thereby diluting their electoral weight and maximizing Republican seat gains.

Progressive pastor William Barber, leader of the Moral Mondays movement, described the new districts as "apartheid voting districts." The changes enabled Republicans to capture nine of the state's thirteen congressional seats in 2012 — even though Democrats cast more votes statewide.

After Republican Pat McCrory's 2012 gubernatorial victory gave Republicans control of all three branches of government, the state GOP tried to lock in its dominance for the long haul. Armed with the governorship, both legislative chambers, and a majority on the state Supreme Court, Republican leaders launched an ambitious string of reforms designed to skew the political game.

They began by demanding access to background data on voters across the state. With this information in hand, the legislature passed a series of electoral reforms making it harder for voters to cast their ballots. They passed a strict voter ID law, reduced opportunities for early voting, ended pre-registration for sixteen- and seventeen-year-olds, eliminated same-day registration, and slashed the number of polling places in several key counties.

New data allowed the Republicans to design the reforms to target African American voters, as a federal appeals court put it, with "almost surgical precision." And when an appeals court suspended the execution of the new laws, Republicans used their control of the state's election boards to implement several of them anyway.

The authors, Steven Levitsky and Daniel Ziblatt. Stephanie Mitchell/Penguin Random House

Institutional warfare persisted after Democrat Roy Cooper narrowly defeated McCrory for the governorship in 2016. McCrory refused to concede the race for nearly a month, as Republicans made baseless accusations of voter fraud.

But that was only the beginning. After McCrory finally conceded in December 2016, Republicans called a "surprise special session" of the state legislature. In a testament to how far politics had deteriorated, rumors spread of an impending "legislative coup," in which Republicans would hand the election to McCrory by exploiting a law allowing legislators to intervene when the results of a gubernatorial election are challenged.

No such coup occurred, but in what the New York Times described as a "brazen power grab," the special session passed several measures to reduce the power of the incoming Democratic governor. The Senate granted itself the authority to confirm gubernatorial cabinet appointments, and it empowered the sitting Republican governor to transfer temporary political appointees into permanent positions.

Outgoing governor McCrory quickly granted tenure to nearly one thousand of his handpicked gubernatorial staffers — essentially "packing" the executive branch. Republicans then changed the composition of the state's election boards, which were responsible for local rules involving gerrymandering, voter registration, voter ID requirements, voting hours, and the distribution of polling places.

The boards had been under the control of the sitting governor, who could award his party a majority of seats; now the GOP created a system of equal partisan representation. In another twist, the chair of the election boards would rotate between the two parties each year, with the party with the second-largest membership (the GOP) holding the chair in even years — which are election years.

A few months later, the legislature voted to shrink the state court of appeals by three seats, effectively stealing three judicial appointments from Governor Cooper.

Although the racially gerrymandered districts, the 2013 voter law, and the reform of the election boards were later struck down by the courts, their passage revealed a Republican Party willing to leverage its full power to cripple its political adversaries. Congressman David Price, a Democrat from Chapel Hill, said the legislative crisis taught him that "American democracy may be more fragile than we realized."

North Carolina offers a window into what politics without guardrails looks like — and a possible glimpse into America's future. When partisan rivals become enemies, political competition descends into warfare, and our institutions turn into weapons.

The result is a system hovering constantly on the brink of crisis.

Excerpted from "HOW DEMOCRACIES DIE" Copyright © 2018 by Steven Levitsky and Daniel Ziblatt. Published by Crown Publishers, an imprint of Penguin Random House LLC.

Steven Levitsky is David Rockefeller Professor of Latin American Studies and Professor of Government at Harvard University. His research interests include political parties and party-building, authoritarianism and democratization, and weak and informal institutions, with a focus on Latin America.

Daniel Ziblatt is Professor of Government at Harvard University and a faculty associate at Harvard's Minda De Gunzburg Center for European Studies. Ziblatt's teaching and research is in comparative politics, with a focus on democratization, state-building, historical political economy, and European politics.