Barack Obama burst onto the national scene with a speech denying the power — denying even the reality — of the deep divisions that seemed to define American politics.

“The pundits like to slice and dice our country into red states and blue states: red states for Republicans, blue states for Democrats,” he said in 2004. “But I've got news for them, too. We worship an awesome God in the blue states, and we don't like federal agents poking around our libraries in the red states.”

His 2009 inaugural speech held to the theme. “On this day, we come to proclaim an end to the petty grievances and false promises, the recriminations and worn-out dogmas that for far too long have strangled our politics. We remain a young nation. But in the words of Scripture, the time has come to set aside childish things.”

This was Obamaism: the theory that the widening gyre between Democrats and Republicans was an illusion whipped up by political consultants, that bitter partisanship was a childish thing that could be put aside to solve America’s toughest problems.

Obamaism was wrong. And now Obamaism is over.

Donald Trump’s inaugural address, like his campaign, was notable in part for how uninterested he was in healing divisions. He did not pretend our disputes were illusory. He did not suggest our divisions would be easy to bridge. He was perfectly clear about whom he was speaking to and whom he wasn’t.

“The forgotten men and women of our country will be forgotten no longer,” he promised. “Everyone is listening to you now. You came by the tens of millions to become part of a historic movement, the likes of which the world has never seen before.”

“You.” This was the most striking word of Trump’s speech. Trump did not use “you” to denote America. “You” was Trump’s America — the people who were part of his historic movement. There was no effort in the speech to reach out to Muslims or immigrants or women or anyone else Trump had scared during the campaign. There was no talk of compromise policies or unexpected alliances. There was no suggestion that political rhetoric had gone too far, and a period of listening, and healing, could now be expected. Even Trump’s mention of dissent came in a vaguely threatening passage:

At the bedrock of our politics will be a total allegiance to the United States of America, and through our loyalty to our country we will rediscover our loyalty to each other. When you open your heart to patriotism, there is no room for prejudice. The Bible tells us how good and pleasant it is when God's people live together in unity. We must speak our minds openly, debate our disagreements honestly, but always pursue solidarity.

Obama took office trying to fight the rising tide of polarization. He spent months, even years, negotiating with congressional Republicans for votes that never came. Trump is not going to waste that time. He is under no illusions that he’ll ever be a unifying figure. He does not think he needs his opponents to like him, and he does not try to win their favor.

Instead, Trump thrives on heightening the divisions in American politics. It’s why he tweets out attacks on Meryl Streep and John Lewis and Hillary Clinton and the “Crooked Media.” The fights he creates are bitter and unnecessary, but they serve to rally his supporters to his side.

If Obama’s contention was that there’s no “them,” only “us,” Trump’s contention is that there really is a “them” — a “them” of immigrants and Muslims and terrorists and Black Lives Matter activists and elites and crooked journalists — and so it’s all the more important for the “us” to stick together.

This is how he won the primary. It’s how he won the election. It’s how he intends to govern. If Obamaism was about strength through unity, Trumpism is about power through division.

Party polarization is how Trump won the presidency

Donald Trump’s nearness to the presidency rests on two separate accomplishments — or, if you prefer, two separate institutional failures — that are often conflated. The first is his victory in the Republican Party’s presidential primaries. The second is his consolidation of elite Republicans, and of the Republican-leaning electorate.

Trump won the GOP primaries with 13.8 million votes. The difference between those 13.8 million votes and the 63 million he won in the general election is vast, and was by no means assured.

In 1972, for instance, George McGovern won the Democratic primary even though much of the Democratic Party viewed him with suspicion and even fear. Major Democratic interest groups, like the AFL-CIO, refused to endorse him in the general election, and top Democrats, including former governors of Florida, Texas, and Virginia, organized “Democrats for Nixon.” McGovern went on to lose with less than 40 percent of the vote, a dismal showing driven by Democrats who abandoned a nominee they considered unacceptable.

A similar path was possible for Trump. Elites within the Republican Party viewed him with horror. His primary opponents spoke of him in apocalyptic terms. Ted Cruz called Trump a "pathological liar," "utterly amoral," and "a narcissist at a level I don't think this country's ever seen." Rick Perry said Trump’s candidacy was "a cancer on conservatism, and it must be clearly diagnosed, excised, and discarded." Rand Paul said Trump is "a delusional narcissist and an orange-faced windbag. A speck of dirt is way more qualified to be president." Marco Rubio called him “dangerous,” and warned that we should not hand "the nuclear codes of the United States to an erratic individual."

And then every single one of those Republicans endorsed Trump. Ted Cruz told Americans to vote for the pathological liar. Rand Paul backed the delusional narcissist. Marco Rubio campaigned to hand the nuclear codes of the United States to an erratic individual. Rick Perry urged people to elect the cancer on conservatism, and today he is preparing to serve as its secretary of energy.

The list goes on. Paul Ryan, the Republican speaker of the House of Representatives, endorsed Trump, as did Mitch McConnell, the Senate majority leader, and Reince Priebus, who was head of the Republican National Committee and is now Trump’s chief of staff. Mike Pence, the governor of Indiana, commiserated with Dan Senor, a former Bush appointee, over the fact that Trump was “unacceptable” — and then became his vice president.

With this kind of elite consolidation, it’s little wonder that Trump managed to consolidate Republican-leaning voters behind him. The final NBC/WSJ poll of the election found that 82 percent of likely Republican voters were supporting Trump — precisely matching the 82 percent of likely Democratic voters supporting Clinton. Trump did not get McGoverned.

As Jon Levy writes of the 2016 election, “We should start by understanding that partisans are very, very likely to vote for their own parties’ candidates, regardless of those candidates’ personal merits or indeed the substance of their views. Republicans will even vote for an opponent of free trade and of the postwar western alliance who grossly offends against conservative Christian sexual mores, if that’s who is at the top of their ticket.”

The bug in American democracy: weak parties, strong partisanship

Political scientist Julia Azari has written the single most important sentence for understanding both Trump’s rise and this dangerous era in American politics: “The defining characteristic of our moment is that parties are weak while partisanship is strong.”

Here is the problem, in short: Parties, and particularly the Republican Party, can no longer control whom they nominate. But once they nominate someone — once they nominate anyone — that person is guaranteed the support of both the party’s elites and its voters. Unlike in McGovern’s day, when ticket splitting was common, any candidate able to win his party’s presidential primaries can now count on his party’s support.

Political parties, and political party primaries, were traditionally bulwarks against demagogues rising in American politics — they were controlled by gatekeepers who acted as checks against charismatic demagogues. Donald Trump would never have made it through the convention horse-trading that used to drive nominations; he would never have survived a process that required support from party officials.

But this also presents a puzzle: If partisans have lost so much faith in their party establishments, then why are they so much likelier to back whomever their party nominates? The answer, in short, is fear and loathing of the other party.

Since 1964, the American National Election Studies have been asking Republicans and Democrats to describe their feelings toward the other party on a scale that runs from cold and negative to warm and positive. In 1964, 31 percent of Republicans had cold, negative feelings toward the Democratic Party, and 32 percent of Democrats had cold, negative feelings toward the Republican Party. By 2012, that had risen to 77 percent of Republicans and 78 percent of Democrats.

Today, fully 45 percent of Republicans, and 41 percent of Democrats, believe the other party’s policies “threaten the nation’s well-being.” This fear is strongest among the most politically involved. Which makes sense: You're more likely to take an active interest in American politics if you think the stakes are high. But that means the people driving American politics — and particularly the people driving low-turnout party primaries — have the most apocalyptic view of the other side.

This is driven by the reality that the two parties have grown more ideologically distant from each other, and so the stakes of elections really have grown larger. In 1994, 34 percent of Republicans were more liberal than the median Democrat, and 30 percent of Democrats were more conservative than the median Republican. Today only 8 percent of Republicans are more liberal than the median Democrat, and only 6 percent of Democrats are more conservative than the median Republican.

And polarization begets polarization. The angrier and more fearful partisans are, the more of a market there is for media that makes them yet angrier and yet more fearful. It is no accident that Steve Bannon, the former CEO of Breitbart News, a hyper-ideological conservative media outlet that specializes in scaring the hell out of its audience, is now Trump’s chief strategist.

Trump’s speech today was all about making his audience angrier and more fearful. “The crime and the gangs and the drugs that have stolen too many lives and robbed our country of so much unrealized potential,” he grimaced. “This American carnage stops right here and stops right now.”

“American carnage.” Those are the words Trump’s speech will be remembered for. They do not describe the reality of America in 2017. But they paint a picture that will keep Trump’s base afraid, angry, and on his side.

The downside of Obamaism and the downside of Trumpism

Trump boasted his inauguration would have an "unbelievable, perhaps record-setting turnout." As the above photograph shows, it did not.

There is no great mystery to this. Trump is unpopular — more unpopular, in fact, than any president elected since the advent of polling. Gallup finds Trump will take office with a 40 percent approval rating. Quinnipiac pegs it at 37 percent. At this point in their pre-presidencies, Obama’s approval rating was 78 percent, Bush’s approval rating was 62 percent, and Clinton’s approval rating was 66 percent.

This is the downside of governing through division: It limits the number of people who can see themselves as part of your coalition, and it makes the opposition loathe you even more. As I write this, there is tear gas on the streets of Washington, DC, as police try to disperse protesters from the path of Trump’s post-inaugural parade.

Obama and the Democrats wasted a lot of time searching for Republican support they never got, and they made a number of unwise substantive compromises along the way. Obamacare, for instance, sat in the Senate for months as Max Baucus sought Republican support, and the subsidies are thinner — and thus the premiums are higher — because Democrats were trying to keep costs down to appeal to Republicans and moderates. In the end, they got no Republican support, and many are frustrated with Obamacare’s high deductibles and premiums.

Trump and the Republicans look unlikely to worry about attracting Democratic support. But they also look unlikely to try to build majority support for their political agenda — a strategy that comes with its own, potentially severe, costs.

The split here may not just be Democrat versus Republican. It might be Trump versus Republican. His inauguration address mostly ignored major conservative priorities like lowering taxes. It’s possible Trump intends to chart a very non-conservative path and rely on the pull of party polarization to sweep his congressional majority along. If Republicans couldn’t stop him from doing and saying what he wanted during the primary, it’s not at all clear they have the backbone or even the political capital to do it now that he’s president.

The price of all this division is, well, division. It is unknown if Trump can hold together a governing majority with such low approval numbers, so little interest in conciliatory rhetoric or legislation, and such an angry, activated opposition. He may prove to be the president who convinces the Democratic coalition that voting in midterm elections really is important — and if so, he will have done the Republican Party terrible, lasting damage. Usually, the strategy of breaking the country in half is pursued by coalitions certain they represent the bigger half; in this case, it’s being tried by the coalition representing the smaller, albeit geographically more efficient, half.

But this is the experiment we began today. Obamaism is dead. Welcome to Trumpism.