The Outrage Machine is a weekly opinion column by voices from the left and right on Washington.

Neither pundits nor political scientists like to admit that they’ve been taken by surprise. But Donald Trump has forced many political experts to admit just that.

Even if Trump loses next Monday’s Iowa caucus, and even if he eventually loses the Republican presidential nomination, his consistent lead in poll after poll was something nobody predicted.

But Trump’s success shouldn’t have been a surprise. It was inevitable.

Last week, when Sarah Palin threw her support behind the wealthy businessman, she emphasized the exact quality that explains his explosive rise. Palin called Trump “a new and independent candidate.” The key word here is “independent.”

It is difficult to pinpoint precisely when the seeds were planted for a viable Trump candidacy, but we can start somewhere in the late 1990’s. Although the media always covered conflict, it was around this time that news coverage of partisan politics took a decidedly negative turn – emphasizing disagreement and stressing partisan polarization. Today, media coverage casts American politics as a snake-pit: in the ongoing battle between Republicans and Democrats, everyone is out for blood and compromise seems impossible.

Of course, the media isn’t pulling this ugly image from thin air – the parties provide ample fodder for all the drama. The increasing ideological polarization in Congress is so well-documented that it has become an axiom of American politics. In our own research, we find that even the language that presidential candidates use in debates has become more antagonistic over time.

Americans are receiving an undeniable message: politicians care more about serving the party establishment than about taking political risks that may help them better represent their constituents. Parties would rather tear each other down than compromise.

In this context, it should not come as a shock that many Americans – both Democrats and Republicans alike — are tired of partisan politics. This message emerged loud and clear as we began work on our book, Independent Politics: Why American Disdain for Parties Leads to Political Inaction

Across dozens of surveys and experiments conducted nationally, we found that Americans may support a party – but they hate themselves for it. Instead, Americans are increasingly seeking to distinguish themselves from the partisan morass.

More often than not, we found that Americans’ dissatisfaction with partisan politics manifested itself in the way they described their own political positions. Time after time people with clear, consistent partisan preferences, people who should say they are Democrats or Republicans, avoid giving any public indication of their partisanship.

This tendency to avoid identification with the two mainstream political parties is not simply a quirk of independent voters. Rather, even people who are begrudgingly willing to admit their partisan preferences still dislike their own party and express disdain for the American partisan establishment.

Given all this, the emergence of a candidate like Donald Trump — and the rise of democratic socialist Sen. Bernie Sanders — stops being an anomaly and more of an inevitability.

If people are sick of parties, then they are also sick of the parties’ chosen candidates. Jeb Bush and Hillary Clinton represent the very establishment that so many Americans are trying to avoid.  These candidates are extensions of the partisan negativity people see around them.

In contrast, Trump, and to some extent Sanders, represent a departure from partisanship — despite the fact that Trump, especially, is slinging negative attacks just like the other candidates.  Trump and Sanders are the counter-partisans. Both candidates have repeatedly demonstrated an unwillingness to follow the very norms of the parties whose nominations they are seeking.

Why are Trump and Sanders so compelling? Because they allow people to reject the establishment without having to leave their own party.

Despite their disdain for parties, most Americans do have a clear preference for one party over the other. Even as they dislike the partisan establishment, most Democrats could never bring themselves to vote for a Republican, just as most Republicans would rather stay home on Election Day than lend their support to a Democrat. In fact, the persistence of support for one party and the dislike for the other is one of the most consistent findings of American political scholarship. As early as the 1960’s, pioneers of American survey research and authors of The American Voter argued that partisanship is influential, persistent, and resistant to change. This is still true today.

Combined with the fact that no recent third-party candidate has ended up with more than 20 percent of the final vote in national elections, this nagging preference for one party over the other makes the possibility of “wasting” a vote on a third-party candidate unattractive.

Trump and Sanders give Americans something they increasingly want: candidates who make them feel like they’re rejecting the party, while still allowing them to remain in the safe, familiar partisan cocoon in which they were hatched. Outsider candidates who run on the party label are like all-inclusive vacations – they involve enough adventure to satisfy the travel bug, but ultimately provide familiar amenities to calm one’s nerves.

So, it should be no surprise that we’re here. After decades of messages about the parties’ troubles and a steady increase in the number of people who refuse to publicly share their partisan affiliation, the sudden enthusiasm for anti-party partisans at the expense of establishment candidates is to be expected.  Even if Trump and Sanders eventually lose to the more tried-and-true options, their rocket-like trajectories should send a shiver down the spine of the establishment.

What our book suggests is the parties would be foolish to dismiss Trump and Sanders as political flukes and anomalies. The parties should worry about Trump and Sanders, and they should also worry about the increasing numbers of partisans who refuse to publicly admit they are partisans.

But the parties should not be surprised by the success of Trump and Sanders – it is the parties who created them.

Samara Klar is an assistant professor of political science at the University of Arizona. Yanna Krupnikov is an assistant professor of political science at Stony Brook University.  They are the author of the book Independent Politics: How American Disdain for Parties Leads to Political Inaction.