Over the past two decades, the internet has lowered barriers to entry in a wide variety of industries. As a result, once-dominant institutions have seen their power — and in some cases their existence — threatened.

In the book industry, Amazon has destroyed traditional booksellers. In the music industry, online services like iTunes and Pandora have undercut the power of traditional record labels. Ride-hailing services like Uber and Lyft have undercut the power of traditional taxicab companies that once had a stranglehold on major urban markets.

Now it's happening in the political system. Social media and a proliferation of online news organizations are undercutting the power of political and media elites, resulting in an electoral system that's more open — and more chaotic — than ever before.

The internet's disruption of the political establishment explains how outsider candidates — Bernie Sanders on the left, Ted Cruz and Donald Trump on the right — have made such huge gains despite the overwhelming opposition of insiders in their respective parties. And it suggests that their rise isn't a fluke. In future elections, insurgent campaigns are only going to become more common, while political insiders will struggle to retain the influence they used to wield.

Insiders used to have a lot of power

If you wanted to win the Republican nomination for president in the late 20th century, it was essential to win the backing of well-connected insiders in the media and political worlds.

Candidates coveted the backing of pundits like George Will and William F. Buckley, and newspapers like the Wall Street Journal and the New Hampshire Union Leader. They courted prominent activists leaders like Grover Norquist and Pat Robertson, and governors and members of Congress in their own party. And they wooed wealthy donors.

These kinds of supporters were partly valuable because they had the respect of rank-and-file voters and party activists. But even more importantly, they controlled resources that were hard for candidates to obtain without their help.

Newspapers had the infrastructure to distribute articles to hundreds of thousands of people. Activist groups had valuable lists of donors and volunteers. Governors and senators sat at the head of political machines that allowed them to mobilize support for their favorite candidates. And well-connected donors could not only write checks themselves but could also invite their wealthy friends to fundraisers.

This was infrastructure and relationships that took years, if not decades, to build. If candidates couldn't persuade elites to help them, they simply had no realistic way of getting their message out, raising significant sums of money, or getting voters to the polls.

Online fundraising is empowering grassroots candidates

Thinking back to the race for the Republican nomination in 2000 illustrates how dramatically the political landscape has changed. George W. Bush leveraged his father's connections and his relatively successful tenure as governor of Texas to lock up endorsements from a large number of conservative elites.

Bush's leading challenger, John McCain, was charismatic, had a compelling message, and generated excitement among voters who saw him speak, allowing him to prevail in New Hampshire. But he simply wasn't able to overcome the financial and organizational advantages conferred on Bush by his supporters in the Republican establishment and the conservative donor class.

McCain was arguably the first presidential candidate to have his campaign catch fire on the internet. In the wake of his upset victory in New Hampshire, McCain raised $810,000 from donors on the internet. At the time, that was considered a shockingly large sum to raise online, but it wasn't nearly enough to allow McCain to build a national campaign that seriously threatened Bush.

But online fundraising has gotten steadily more important for insurgent presidential candidates. In 2004, internet darling Howard Dean shocked the political establishment by raising $5 million a month in the final six months of 2003, much of it online. In December 2007, Ron Paul supporters organized an online "money bomb" that raised $6 million in a single day — without the campaign having to lift a finger.

In the current election cycle, Hillary Clinton has the same kind of overwhelming support among insiders that George W. Bush enjoyed 16 years ago. But thanks to the internet, that hasn't stopped Bernie Sanders from putting up a serious fight. He was able to leverage his online support to raise $73 million from 1 million donors in 2015 — most of whom gave small amounts. He raised another $20 million in January and $40 million in February, with an average contribution size of $27.

On the Republican side, Jeb Bush tried to replicate his brother's strategy this election cycle, raising more than $150 million in campaign and Super PAC funds. But these early advantages seemed not to help him at all, as he quickly fell behind outsiders Ted Cruz and Donald Trump.

How the internet boosted Bernie Sanders

In late 2014, just as politicians were starting to lay the groundwork for their presidential campaigns, we at Vox started to notice that articles about Bernie Sanders attracted a lot of traffic. And it wasn't hard to figure out why: Bernie Sanders fans love reading articles about their favorite candidate and sharing them with their friends.

The internet's appetite for Bernie content has only increased over the past 18 months. Last Wednesday — the morning after this week's primaries in Michigan and Mississippi — I took a snapshot of the popular /r/politics subreddit, a section of Reddit devoted to politics:

This subreddit is supposed to focus on US politics generally, so you might expect some pro-Clinton articles and perhaps even some pieces about Republican presidential candidates. But stories on Reddit are chosen by users' votes, and the /r/politics subreddit is dominated by Bernie Sanders fans.

The result: /r/politics focuses almost exclusively on the Democratic side of the presidential race (only two headlines mentioned a Republican presidential candidate, and one of them was about how Sanders was the best candidate to beat Donald Trump). And articles overwhelmingly take a pro-Sanders point of view.

About a year ago, news sites learned that pro-Bernie content generated a lot of traffic, and many started producing more of it. That, in turn, spread the word about the Sanders candidacy, attracting new supporters and further expanding demand for pro-Bernie content.

Social media creates filter bubbles

Sanders was able to broaden his appeal among liberals despite the fact that many prominent liberal pundits — including Paul Krugman, Jonathan Chait, Kevin Drum, and Jamelle Bouie were attacking Sanders for having half-baked policy proposals and an unrealistic political strategy. One big reason these attacks failed is that a lot of Sanders fans never saw them.

People on /r/politics aren't just reading more articles about Sanders, they're also overwhelmingly getting articles that are pro-Sanders. Articles that criticize Sanders or make the case for Hillary Clinton (or, for that matter, any of the Republican candidates) are much less likely to reach the front page.

And this doesn't just happen on Reddit. Similar things tend to happen on social media sites like Facebook and Twitter. These sites are all about sharing with your friends. And because people tend to have similar politics as their friends, this means social media tends to reinforce what people already believe.

"It's easier than ever to surround yourself with information that confirms what you already believed was true," says Eli Pariser, a liberal activist who founded the social news site Upworthy. In a 2011 book, Pariser dubbed this phenomenon a "filter bubble."

Last year, researchers at Facebook documented the extent of this phenomenon. Liberal Facebook users see more liberal articles on their newsfeeds. Conservatives see more conservative articles. The Facebook researchers argued that this wasn't really Facebook's fault — it simply reflects the kinds of friends people have and the kinds of articles they share. But regardless of whose fault it is, the result is the same.

Donald Trump is a master at manipulating cable TV

I'm not the first to wonder whether the 2016 campaign is being driven by the phenomenon Pariser described five years ago. Last month, Slate's David Auerbach argued that the echo chamber of social media had helped push Democratic voters to the left, creating fertile ground for the Sanders revolution.

And of course you could tell a similar story on the political right; Donald Trump is the most popular presidential candidate on Twitter, with 6.8 million followers, and that can't have hurt his bid for the Republican presidential nomination.

But Pariser is skeptical of this theory. "I think there are pieces of it that are overplayed," he told me. He doesn't believe that either Trump or Sanders is primarily a social media phenomenon because "social media is not the place where they make contact with a mass audience."

This point seems particularly compelling for Trump. As Pariser pointed out to me, Trump spends a lot of time calling in to cable news shows. He is also popular among conservative talk radio hosts. It's this coverage, as much as his popularity on Facebook and Twitter, that helped power his rise.

Social media has aided Trump's rise

But while the internet wasn't entirely responsible for Trump's success, it has done a lot to weaken the influence of conservative elites and undermine their ability to organize a stop-Trump movement.

Back in January, the prominent conservative magazine National Review devoted an entire issue to the case against Trump. It invited a wide variety of conservative luminaries to contribute articles urging voters to reject him. That came on top of almost nonstop attacks on Trump from Fox News and conservative columnists like George Will and Charles Krauthammer.

The internet has done a lot to weaken the influence of conservative elites

In the pre-internet era all of this would have been pretty damaging. For some conservatives, National Review was the only conservative news source they read, and a lot of local conservative columnists took their cues from the magazine. Other conservative voters would have been regular viewers of Fox News or regular readers of nationally syndicated columnists.

Without a national media platform of his own, a pre-internet Donald Trump would have struggled to get a response out to his supporters. Even conservatives who liked Trump's message would have hesitated to support him in the face of apparently united conservative opposition.

Things are very different in the internet era. Online, National Review is simply one of many sources of conservative news and opinion. There are other online news sources like Breitbart that are pro-Trump. Breitbart isn't as prestigious as National Review, but because of social media that doesn't matter very much — Breitbart articles can be shared on Facebook and Twitter as easily as National Review articles can, and a lot of readers aren't going to know the difference.

Even more importantly, Trump has a Twitter account with 6.8 million followers. When National Review attacked him, he was able to respond immediately, and more people may have seen his response than the original attack.

National Review is a failing publication that has lost it's way. It's circulation is way down w its influence being at an all time low. Sad! — Donald J. Trump (@realDonaldTrump) January 22, 2016

The disruption of politics has a downside

If you're a supporter of Donald Trump, Ted Cruz, or Bernie Sanders, you probably find all of this exhilarating. Finally, grassroots activists are breaking up the cozy relationship between Washington insiders and their allies in the elite media.

But there are also some downsides to the declining influence of elites. Scurrilous rumors spread more easily. It's harder to hold candidates responsible for their misstatements.

Many elite economists — including those who have served in previous Democratic administrations — think the Sanders campaign is massively overstating the economic benefits of his domestic policy agenda. Even supporters of universal health care think the numbers don't add up on Sanders's universal health care plan. And as Vox's Matt Yglesias has put it, his free tuition plan is half-baked.

On the right, Republican candidates have been proposing tax plans that are several times as large as the George W. Bush tax cuts. Maybe you think big tax cuts are a good idea, but candidates like Marco Rubio and Ted Cruz have also been pledging to boost military spending and balance the budget. There's no way they can deliver on all these promises simultaneously.

Political and media elites tend to care about this sort of thing, and in the pre-internet era Sanders, Rubio, and Cruz would have faced a lot of pressure to produce plans that add up. But candidates are becoming less and less dependent on conventional media outlets to get their message out. They can count on more partisan media outlets and direct social media communication to get their message to their supporters — without having to answer a lot of awkward questions about wonky details.

So candidates have less incentive than ever to back up their campaign rhetoric with detailed policy proposals and numbers that add up. Donald Trump can run on a slogan like, "Build a wall and make Mexico pay for it," without making any real effort to explain how he's going to do that.

The disruption of politics is just getting started

The remarkable thing about this is that the disruption of traditional media is still in its early days. Traditional newspapers, magazines, radio broadcasts, and television networks still reach large audiences. Donald Trump's rise was aided as much by his popularity on cable television as on social media.

This means that social media's disruption of politics is only going to accelerate in the next few elections.

"The way that stories get told in our society is still predominantly driven by broadcast media," Pariser says. "Yes, social media is having a bigger and bigger impact, but it hasn't yet moved into primacy."

It's impossible to predict what the next phase of the social media revolution will look like. Maybe cable news channels will get displaced by streaming channels hosted by YouTube or Netflix. Maybe talk radio will get displaced by podcasts.

But one safe bet is that the media of the future will be even more decentralized than today's media. It will be easier than ever for voters dissatisfied with the status quo to find each other, organize, and back political outsiders willing to champion their concerns.

Pariser predicts that when the political process finally feels the full impact of the internet revolution, it will be "more like a phase change than just an incremental shift." The Trump and Sanders campaigns might seem like a dramatic change from the status quo, but the internet's political revolution is just getting started.

Correction: I stated that Sanders had 2.5 million donors in 2015, when he actually had 2.5 million donations.

A look back at the rise of Bernie Sanders