On May 30, 11 days before one of the biggest upsets in modern American politics blocked Majority Leader Eric Cantor’s path to speaker of the House, one of his top aides emailed me in an unusually defensive tone. Doug Heye, Cantor’s deputy chief of staff, had a “quibble” with an analysis I had written for the Cook Political Report on the state of play in the GOP primary for Cantor’s congressional district.

In my analysis I wrote, “Economics professor [and Cantor’s primary opponent] Dave Brat has forced Majority Leader Eric Cantor to take his primary very seriously.” Nonetheless, relying on what turned out to be flawed private polling, I had also noted that Cantor wasn’t anywhere “near the danger zone.”

Still, Heye emailed to say, “Saw your ratings. One quibble — Brat has not forced Cantor to take the primary seriously. He takes every election seriously and, in fact, began advertising last cycle even earlier. Eric Cantor is simply incapable of phoning anything in.”

I predict House races 365 days a year for a living, so defensive emails from campaigns like this one aren’t out of place. On election night, when it was clear from the first few precincts that David had slayed Goliath, I was just as shell-shocked and knew immediately that the results would force me to rethink my entire approach to handicapping primaries. But I couldn’t help but think of Heye’s email with amusement.

Perhaps Heye was correct that Cantor took “every election seriously.” By the time the primary rolled around, Cantor had been running ads attacking Brat for more than a month. In fact, the biggest myth on Twitter on election night may have been that Cantor was “blindsided.”

But Cantor’s downfall proves taking “every election seriously” isn’t the same thing as being “incapable of phoning anything in.” For Cantor and his advisers, taking the election “seriously” meant brutally defining Brat (through lots of television ads) before the “liberal college professor” could ever hope to define himself. To suburban Richmond primary voters, who were well aware of their congressman’s Capitol ambitions, that strategy may have looked like he was phoning it in.

In truth, when an election result hits “10 on the political Richter scale” of shock value, there usually isn’t just one reason for the outcome, but lots of them acting in concert. While surveying the wreckage, Cantor adviser John Murray acknowledged his boss’s loss amounted to “death by a thousand cuts.” None of these reasons alone would be sufficient to cause an upset, and some of them aren’t neatly quantifiable. But there are plenty of ways to dissect what happened in Virginia’s 7th district, as well as some lessons we political forecasters would be wise to keep in mind in the future. Here are just a few.

1) Public disgust with Congress was a necessary prerequisite for Cantor’s defeat.

Public disapproval of Congress as a whole has achieved such heights that it almost can’t get any higher. But Gallup has asked two incredibly useful questions of voters since 1992: whether they would vote to re-elect their own member of Congress, and whether most members of Congress deserve re-election.​

It’s not surprising that voters have always liked their own member of Congress better than Congress as a whole. But what’s most striking are voters’ shift in attitudes since 2012 on the question of their own member: In 2012, more than half of voters said they would still vote to re-elect their own member of Congress, but by January of this year that share fell to 46 percent.

Since primary season began in March, that decline has manifested itself quietly, but powerfully.

Cantor was only the second House incumbent to lose a primary this year (the first was Texas Republican Ralph Hall), but the warning signs of discontent were abundant: Plenty of rank-and-file House incumbents had been receiving startlingly low primary vote shares against weak and under-funded opponents, including GOP Reps. Rodney Davis of Illinois, Lee Terry of Nebraska and David Joyce of Ohio. In fact, just a week before Cantor’s defeat and without much fanfare, socially moderate Rep. Leonard Lance of New Jersey received just 54 percent of the Republican primary vote against the same tea party-backed opponent he had taken 61 percent against in 2012.

Overall, 32 House incumbents have taken less than 75 percent of the vote in their primaries so far this year, up from 31 at this point in 2010 and just 12 at this point in 2006. What’s more, 27 of these 32 “underperforming” incumbents have been Republicans.

In other words, while Congress’s unpopularity alone can’t sink any given member in a primary, it has established a higher baseline of distrust that challengers can build on when incumbents are otherwise vulnerable. And as the sitting House Majority Leader, Cantor was uniquely susceptible to voters’ frustration with Congress as an institution.

2) Cantor’s home base wasn’t ever as comfortable with him as most people thought.

One rule of politics is that voters generally like to vote for candidates who can relate to them. Whether it’s a matter of race, ethnicity, religion, lifestyle or simply shared life experiences, identity politics can be extremely potent. To his credit, Cantor never pretended to be someone he wasn’t, but in many ways he was culturally dissimilar from his own primary base.

Although Cantor’s district is a diverse mix of wealthy Richmond suburbs and rural, gun-owning counties, it’s safe to say the average GOP voter in the district is a church-going suburbanite more likely to, say, dine at Cracker Barrel than shop at Whole Foods. Cantor’s persona drifted from this reality over the course of his tenure: He is suave, polished, and came to be known for raising lots of money at upscale D.C. steakhouses and in New York City.

Cantor is also the only Republican in the House who attends synagogue, not church. After his loss, I made an assertion in a New York Times article that part of this cultural disconnect “plays into his religion,” which ignited a small social media firestorm. To clarify, by no means was I alleging that the district’s primary electorate is the least bit anti-Semitic.

However, in countless southern primaries, Christian GOP candidates have emphasized their religious values and used evangelical language and imagery to establish a connection and comfort level with primary voters. This is something Cantor could never do, and he tended to emphasize his family over his faith. His opponent, Brat, however, earned a business degree from Hope College (a small Christian school in Michigan) and a divinity degree from Princeton Theological Seminary, and referred to his victory as a “miracle,” adding, “God gave us this win.”

Dozens of people on Twitter have countered this idea with some variation of this question: If Cantor’s cultural dissimilarity was to blame, how did he keep winning for 14 years? The answer is that he was never really challenged. In 2000, Cantor’s last competitive race, he won by just 263 votes in the primary over state Sen. Stephen Martin, a social conservative who only raised about a quarter of the money Cantor spent but had strong support from evangelicals. And that was before Cantor was saddled with the epithet of “Washington insider.”

Then, in the Republican landslide of November 2010, another warning sign went largely unnoticed: While most other House Republicans in similarly safe seats were winning re-election in excess of 70 percent of the vote, Cantor took only 59 percent, with an “Independent Green” candidate, Floyd Bayne, taking 7 percent. Bayne spent almost nothing but ran strongest in the portions of the district that were most heavily Christian conservative.

3) Cantor realized he’d have to work with Democrats to actually govern, and his new tone didn’t hold up back home.

Over the last few years, it became more apparent to Cantor that if he became speaker of the House he’d need to work with Democrats to govern, while also presiding over a seemingly ungovernable GOP. He slowly evolved from Speaker John Boehner’s top rival into a more conciliatory conservative, willing to make deals, for example, on the debt ceiling. He also began devoting more time and energy to articulating conservative policy alternatives than most of his peers in the Republican conference.

Cantor privately chastised tea partiers in his conference who fomented the 2013 government shutdown, came out in favor of restoring parts of the Voting Rights Act, and helped craft a watered-down DREAM Act that would provide a path to legalization for immigrants who came to the U.S. illegally as children. But he seemed to do so with fairly little regard to how rock-ribbed conservative primary voters back home would react to these pragmatic gestures.

A few weeks before the primary, Cantor’s campaign sent out a mailer billing him as a hero in the fight against “amnesty” for “illegal aliens.” The only problem? The average GOP voter in his district who shows up in a June primary is relatively well informed, which means she would have known that Cantor supported some immigration reforms. Most voters could sniff out the hyperbole, viewing Cantor’s over-the-top language as desperation.

4) Sometimes it pays to “kneecap” an unknown opponent, and sometimes it backfires.

In the early spring, Cantor’s campaign faced a tactical fork in the road: Would it simply stay positive, emphasizing Cantor’s conservatism while ignoring the unknown and underfunded college professor running to his right? Or would it cut out Brat’s legs early (much as President Obama did to Mitt Romney in 2012) by defining him negatively in an attempt to stop him from gaining any traction whatsoever?

In hindsight, it’s easy to say Cantor’s decision to wallop Brat on the airwaves was an epic blunder. But considering today’s high antipathy toward Congress, this fork in the road presents a difficult dilemma for many incumbents. And several, such as GOP Reps. Mike Simpson of Idaho and Bill Shuster of Pennsylvania, have gone negative effectively and won. The difference? Simpson and Shuster mostly had effective and substantive lines of attack against their opponents. Cantor did not.

Cantor’s decision to attack Brat as a “liberal college professor” and ally of Democratic Sen. Tim Kaine was immediately called out by FactCheck.org as inaccurate, and most voters with access to Google could have found out in seconds that Brat wasn’t the least bit liberal and hadn’t advised Kaine. The ad barrage not only generated curiosity about Brat, it may have created sympathy for him.

5) Voters still need some tender loving care, no matter how high-ranking their representatives in D.C. are.

For most longtime House incumbents, the task of winning a primary is roughly equivalent to an NBA player following through on a layup. It’s an easy shot, but requires a soft touch. Voters don’t like to be taken for granted, and they need a little attention every now and then to know that their leaders, however powerful or high on the congressional leadership ladder, still “care about them.” By nearly all accounts, Cantor blew the layup.

Contrast Cantor’s efforts with John Boehner’s. The Ohio Republican’s primary campaign was against a tea party challenger, Christian college employee J.D. Winteregg. Winteregg had little money, but ran a memorable low-budget ad playing on Boehner’s last name, entitled “Electile Dysfunction.” Rather than engage Winteregg, Boehner ran simple positive ads, spoke at a local chamber of commerce, and shook hands at diners.

Cantor might have been better off following Boehner’s example and adopting a more suitable “home style,” as Sean Trende has alluded. A seemingly silly blog item on Boehner’s campaign website pictured Boehner at a local diner and said, “When John Boehner finds a diner he likes, he sticks with it. That’s why John made sure to stop by Eaton Place this morning before meetings with constituents and small businesses.” This kind of kitsch seems innocuous, but it’s satisfying comfort food for voters.

6) When polling is sparse, one bad poll can poorly set conventional wisdom.

At 7:30 p.m. on June 10, when it was clear to the small group of Twitter nerds who intimately study Virginia precinct-level voting behavior (myself included) that Cantor was going down, not a single cable TV network was prepared for the possibility he could lose. The conventional wisdom pointing to Cantor’s safety was largely generated by one poll taken for the majority leader’s campaign by pollster John McLaughlin in late May showing Cantor leading Brat 62 percent to 28 percent.

Those of us who have tracked McLaughlin’s results in House races have come to digest his data with several grains of salt. But could a pollster really be 45 points off the mark two weeks out? It strains credulity. Brat clearly owned momentum over the last fortnight, but most GOP operatives now blame McLaughlin’s poor sampling for his misleading numbers. Nonetheless, the poll had the effect of “waving off” both Cantor allies and the press from the race.

McLaughlin’s subsequent assertion that Democratic voters skewed the race by crossing over to vote for Brat in Virginia’s open primary was just as farfetched as his polling. Were there some Democrats who crossed over for Brat to “stick it” to Cantor? Absolutely. But a close look at precinct-level results offers little evidence that Democrats participated at anywhere near high enough levels to affect the outcome.

Nate Cohn’s extensive analysis of the primary at The Upshot meshes with these findings and makes clear that Brat owes his strongest performances to Republican voters living in deeply conservative precincts, not Democrats such as former Dukes of Hazzard star Ben “Cooter” Jones, who urged voters on the left to play the role of spoiler. In the 58 district precincts President Obama carried in 2012, turnout in the 2014 GOP primary was up 42.7 percent over 2012. Brat took 58.1 percent of the vote in these precincts. But turnout jumped by roughly the same amount (42.8 percent) in the 37 precincts where Obama received between 30 and 35 percent of the vote. And Brat got a higher share of the vote (59.4 percent) with a much larger raw vote margin in the 33 precincts where Obama took less than 30 percent.

The lesson I and others will take away: Don’t jump to easy conclusions in volatile primary situations where good polling is in short supply.

7) The primary played out on media ignored by most Beltway pundits.

Today’s polarized media environment heightens the odds that a candidate earning buzz within his own ideological echo chamber can fly under the radar of most Beltway pundits. I learned this lesson the hard way in Cantor’s race.

When I’m looking for trustworthy news on local Virginia politics, I’ve typically turned to the Washington Post, the Richmond Times-Dispatch and a handful of blogs I consider to be down the middle. But what if the voters who actually show up for a partisan primary are consumers within an entirely different media ecosystem? When conservative media personality Laura Ingraham showed up at a 500-person Richmond rally for Brat the week before the election, the cash-strapped crop of traditional local outlets didn’t cover it. But Breitbart.com sent reporter Michael Patrick Leahy to the scene, and ran an extensive article with the provocative headline “Laura Ingraham: We Should Have Traded Cantor for Bergdahl.”

Breitbart.com and conservative radio host Mark Levin rallied to Brat’s cause at the eleventh hour, but most Beltway pundits don’t voraciously read or consume partisan media because, well, it’s just that. However, as more American elections are decided in the primary instead of the general election, the importance of watching, listening to or reading both conservative and liberal outlets for clues will continue to rise, no matter the outlet’s editorial integrity.

Bonus takeaway: Cantor’s loss proves there are limits to strictly data-driven election predictions.

Effective election forecasting is necessarily a mix of art and science. In the case of Cantor’s district, there weren’t traditional quantifiable metrics or shortcuts (fundraising reports, polls or ad dollars spent) that would have suggested a Brat victory. To truly grasp how Republicans were shifting on Cantor, an observer would have needed to see firsthand what was happening on the ground, which is exactly what Washington Post reporters Jenna Portnoy and Robert Costa did so well in early May.

Although I and almost everyone else failed to predict it, the Cantor earthquake does offer important reassurances. First, great shoe-leather reporting and sound polling analysis aren’t rivals; they must go hand in hand. In this case, Portnoy and Costa’s dispatches helped paint a more complete portrait of the race than the top-line numbers of any one poll. Second, voters are smarter and more discerning than we often give them credit for, and aren’t always swayed by one candidate who vastly outspends another.

Finally, the next time a high-ranking aide tells me that his boss is “simply incapable of phoning anything in,” I’ll know an exciting upset could be lurking around the corner.