Donald Trump’s impending inauguration is a crowning achievement for a man who went from a cultural curiosity at the start of the 2016 campaign to an unexpected president-elect. But it’s also the pinnacle of a mass political movement lying just under the surface of American politics until he emerged.

That movement, as described in our “United States of Trump” series, turned into a geyser of votes, enough to skate through the Republican primary contest and topple Hillary Clinton, the best known Democrat in America. Trump won his Electoral College victory thanks to about 80,000 voters in three states — Michigan, Wisconsin and Pennsylvania — but he also lost the popular vote by more than 2.8 million, reflecting the deep divide in the country over his impending presidency.

Trump’s power famously came from his “silent majority” — working-class white voters who felt mocked and ignored by an establishment loosely defined by special interests in Washington, news outlets in New York and tastemakers in Hollywood. He built trust within that base by abandoning Republican establishment orthodoxy on issues like trade and government spending in favor of a broader nationalist message.

Trump’s power famously came from his “silent majority.”

Trump’s appeals to the economic, cultural and racial fears of his supporters were widely perceived as offensive to women and minorities. Many GOP leaders warned it would be impossible to win a national election by polarizing the electorate and focusing so intensely on a shrinking segment of the population, even as the country is becoming more diverse, educated and culturally tolerant.

Trump proved them wrong.

Our series captured the emerging Trump coalition and covered the roots of his surprise victory as it unfolded, first examining the nuances of his popularity with Republican primary voters, then analyzing the historic tensions simmering in the GOP reflected by his candidacy and finally looking at the competing future directions available in what Trump exposed as a fractured party.

The Rise of Trump’s Silent Majority

Trump won the presidency the same way he won the primaries: with the support of a loyal, mostly homogenous core of voters who had previously felt ignored from the political process and disconnected from America’s advancements.

The Rust Belt Region Once a manufacturing hub, this section of the country has been struggling with population loss, job loss and income stagnation. Rust Belt

The base of primary voters Trump cultivated, described in-depth in chapter one, stayed with him and then expanded, ultimately taking him past Clinton and breaking through the longstanding Democratic “Blue Wall” in Wisconsin, Michigan and Pennsylvania — swing states lost to Republican presidential hopefuls for nearly three decades. Throughout the Rust Belt, which Obama comfortably carried in 2008 and 2012, Trump racked up massive backing in blue-collar counties that surmounted Clinton’s stronger showing in the cities and more white-collar suburbs.

Clinton maintained slight advantages in what had previously been general-election bellwethers like Hamilton County in Ohio, Bucks County in Pennsylvania and Oakland County in Michigan. It’s likely Trump’s harsh comments on immigration helped Clinton improve on Obama’s performance with Latinos in states like Arizona and Texas, where she significantly closed the gap from 2012 but still came up short.

Trump won the presidency the same way he won the primaries: with the support of a loyal, mostly homogenous core of voters.

On the other side of the ledger, though, Trump’s candidacy fueled a decisive surge in turnout in rural and working-class counties and in areas where the percentage of people over age 55 is higher than the national average. Furthermore, 1.4 million more people from those areas voted in 2016 than four years ago, according to the American Communities Project. Exit polls showed a 14-point swing among whites without a college education toward Trump versus Romney’s 2012 performance. Critically for Trump, his appeal resonated with voters in states that are key to winning the Electoral College.

This shift was easily spotted at the county level. For instance, in small, working-class Juneau County, Wisconsin, home to 26,500 people, Trump bested Clinton by 26 points. President Obama won the county by 7 points four years ago. In Macomb County, Michigan — a blue-collar Detroit suburb home to 855,000 people — Trump won by more than 11 points. Obama won it by 4 points in 2012. And in Lackawanna County in northeast Pennsylvania, typically a critical county for Democrats in the battleground state, Clinton won, but barely, beating Trump by less than 4 points. Obama won the county four years ago by over 27 points.

The Counties Donald Trump Swung Most Difference between the percentage of votes the Republican candidate received in 2012 and 2016. Circles are sized by the difference between the percentage of votes the Republican candidate received in 2012 and 2016. The bigger the circle, the larger that county swung republican.

Ultimately, Trump won not only because of a blue collar surge but because he was able to unite his party — consolidating support from Republican voters who had expressed misgivings about his candidacy. He won 90 percent of GOP voters in the general election, according to exit polls.

It’s Trump’s Party Now

Trump did what candidates like Ross Perot and George Wallace had tried and failed: He won on a populist message. Speaking directly to working-class strongholds, Trump fired up voters who felt left behind by globalization, and he helped to polarize opinion with unusually naked appeals to bigotry and fears of cultural change.

As chapter two of the series examined, the Republican Party has for decades been plagued by tensions between free market conservatives and populist movements that manifested in the insurgency of Reagan’s first presidential run in 1976, the popularity of Perot in 1992 and the growth of the tea party movement in 2010. These movements have always been a reaction to economically challenging times or dramatic cultural and societal shifts. But as chapter two noted, these populist eruptions in modern politics have only narrowly influenced shifts in policy or political behavior. Eventually they get sucked back into the behemoth of the business-oriented GOP or recede back into political oblivion.

In chapter three of this series, we talked to conservatives across the spectrum of the Republican Party to outline four possible scenarios of what the GOP might look like after 2016 and perhaps far beyond that. Some, like Trump, saw a less ideological and more populist emphasis as the party’s natural direction even as some disagreed with Trump’s spin on it. Others saw a party that was both more purely conservative and more welcoming to educated professionals, minorities and young people.

With Trump’s victory, “Trumpism” has won. But Trump’s notoriously slippery and often contradictory answers on how he’d govern sets up a debate over what “Trumpism” actually means. It’s a debate that will continue into the next four years.

Trump’s often contradictory answers on how he’d govern sets up a debate over what “Trumpism” actually means.

Because many policy debates between Trump, the party’s traditional conservative wing and other factions have not yet been resolved, it’s not yet clear how the president-elect and the Republican Congress will govern. Will Trump follow the lead of establishment conservatives like his incoming chief of staff Reince Priebus, Vice President-elect Mike Pence and House Speaker Paul Ryan, whose agendas are broadly in line with the pre-Trump GOP? Or will Trump’s senior adviser Steve Bannon, who has called for major government spending to create jobs while simultaneously espousing an angrier anti-Washington message, prevail? Or could Trump even forge a working coalition on key issues with Democrats, who have shown some interest in testing his independence?

For now, Republicans insist they stand united. Just two days after Election Day, Trump spent an afternoon on Capitol Hill, meeting with Senate Majority Leader Mitch McConnell and Speaker Ryan. They walked together in front of a throng of press down the historic halls of Congress, praising the progress made in the meetings and signaling unity.

But a number of challenges are already on the way. Trump said during the campaign he favors a more interventionist approach by government than do Republican congressional leaders, and Trump has signaled he wants to preserve certain aspects of Obamacare rather than push a wholesale repeal.

Trump has also pushed back on cutting entitlement spending, an effort long backed by traditional conservatives. Yet despite Trump’s stated position, Ryan has continued to talk up his longstanding plan to overhaul Medicare. Trump has also advocated a $1 trillion effort to rebuild the country’s infrastructure, not unlike the stimulus program Obama championed and that Republican lawmakers largely opposed. In foreign policy, Trump splits with his party in some respects, especially in his lack of skepticism of Russia, but Trump’s international positioning has been mostly inconsistent, leaving Republicans uncertain of his next international move.

Trump’s victory was so narrow that it’s difficult to attribute any one factor to carrying him across the line.

As mentioned in chapter three, tax policy will be a defining debate for the Republican Party. The party consensus since Reagan has emphasized tax cuts for the wealthy as a way to spur economic growth, but some reformers have proposed abandoning this approach in favor of targeted benefits for working families instead. Trump ran on both sides of the issue: He said he supported higher taxes on the rich, but released two multi-trillion-dollar tax plans that overwhelmingly benefitted top earners.

The Uncertain Future

Trump’s victory was so narrow that it’s difficult to credit any one factor with carrying him across the line. That also makes it hard for both parties to move into the future.

If Trump’s win heralds a decisive trend in which white working class voters support Republicans by ever-expanding margins, he could remain a heavy favorite for re-election in 2020 even as the country becomes more racially and economically diverse. Democrats, for their part, could be caught between a Sun Belt moving their way in places like Georgia and Arizona to make up for the Rust Belt’s Republican drift, but not fast enough for a Democratic candidate to win nationally.

It’s also possible that Trump’s win is part of a global phenomenon of populist and nationalistic policies and leaders that have caught fire with voters worried about the ongoing threat of international terrorism, increased immigration and economic inequality. Their growth abroad suggests the Trump phenomenon may be durable and go beyond his personal appeal.

But it could be Trump’s election was more of a fluke, a razor-thin victory that any of a number of factors could have reversed. Clinton, like Trump, was an unpopular nominee, and depressed Democratic turnout in close races like Michigan and Wisconsin undoubtedly helped Trump win.

The biggest unknown factor, though, is simply how Trump performs as president. He starts with a skeptical electorate — exit polls showed only 33 percent of voters found him honest, and just 35 percent said he had the temperament to be president — and will have to prove that he can translate his message of radical change into positive results. For an incumbent president seeking re-election, there’s no substitute for success.