The axiom is so often used to explain away accurate but embarrassing poll results that it sounds too cliché to use it in most cases, but it’s true — the only poll that matters is the one on Election Day. Eric Cantor proved that last night, much to his chagrin, after his campaign bragged last week about an internal poll showing him up 34 points against his primary challenger, Dave Brat. Despite being outspent 25:1 in the primary — that’s not a typo, but twenty-five to one — Brat prevailed by beating Cantor by eleven points in an unusually high turnout.

So … what happened? John Avlon writes that the Tea Party that Cantor encouraged came back to bite him, and that the primary process itself is to blame:

First-time candidate and full-time economics professor Dave Brat decisively defeated the consummate pol by a 55 to 45 margin. His secret? Run hard to Cantor’s right on immigration and other hot button issues while boasting the support of talk-radio favorites like Mark Levin and Ann Coulter.

But don’t give the TeaVangelist team too much credit for strategic genius. The key factor in this upset is a 12% voter turnout—meaning that 6.1% of the local electorate could make a majority. This is a paradise for activists and ideologues—Main Street voters, not so much.

No one seriously doubts whether Cantor could have won a general election in his Virginia district. This is purely a numbers game. An unrepresentative turnout makes for an unrepresentative result. And for Republicans, it is perhaps the most pointed reminder of the dangerous game they’ve been playing by stoking the fires of furious conservative populism. Golem ultimately turns on its creator.

Sorry, but this is absurd. First, Cantor himself got elected through the same supposedly unrepresentative process of the primary system. Second, what would be more representative to determine a party nominee — a caucus? Living in a caucus state myself, I can assure Avlon that’s not the case; caucuses are much more prone to get hijacked by small and unrepresentative groups who are effective at organizing. Just because people don’t choose to vote in primary elections (or city elections, or judicial elections) doesn’t make them unrepresentative. All eligible voters can vote if they choose to do so, and if they don’t, that’s their business too. The winner represents that choice as well.

Also, it should be noted that turnout in this primary was actually higher than those earlier primaries that nominated Cantor (almost 20,000 more than in 2012) and were supposedly more representative — and that Cantor got fewer votes this time than in his last primary. In fact, Cantor’s pollster relied on those dynamics to explain how he got the race wrong by about 45 points in the gap:

The survey had Cantor ahead of his opponent, little-known professor David Brat, 62 percent to 28 percent, with 11 percent of voters undecided, according to the Post. It polled 400 likely Republican primary voters on May 27 and 28.

It was supposed to have had a margin of error of 4.9 percentage points. The error, of course, was far larger. (Statistically, this is expected to happen on 1 in 20 surveys.) In the end, it undercounted Brat’s support by about 27 percentage points and overestimated Cantor’s by 17 points. The poll was widely mocked on Twitter.

In an email to National Journal, McLaughlin, whose firm has been paid nearly $75,000 by Cantor’s campaign since 2013, offered several explanations: unexpectedly high turnout, last-minute Democratic meddling, and stinging late attacks on amnesty and immigration.

“Primary turnout was 45,000 2 years ago,” McLaughlin wrote. “This time 65,000. This was an almost 50% increase in turnout.”

Translation: McLaughlin’s estimate of who was a “likely Republican” voter was way, way off the mark. But Cantor’s total number of votes still shrunk, even as the total number of primary voters went up dramatically in 2014. He secured 37,369 primary votes in 2012 and less than 29,000 this year, with 100 percent of precincts reporting.

That negates Avlon’s complaint, and McLaughlin’s other excuse, which is that the new voters may have been primarily Democrats. Virginia allows crossover voting, and Democrats did encourage their voters to do so, but it seems rather unlikely that this caused Cantor to lose votes, especially to Brat, when Democrats don’t have a marquee candidate to face Brat. (They have one of Brat’s colleagues at Randolph-Mason, Jack Trammell, as their nominee.)

The Washington Post probably comes closest to the mark on what created the problem:

Several said they believed that Cantor had mismanaged his campaign, with a strategy in which he was too aloof and his tactics too aggressive. In Virginia, some Republicans perceived him as having grown removed from his 7th Congressional District, spending too much time on national fundraising and Washington infighting.

“Cantor’s field effort was nonexistent. You didn’t see a heavy Cantor presence at Shad Planking, one of the premier Virginia GOP events, and the movers-shakers in the group he works with, YG Virginia, did not have the staff to fully compete,” said Andrew Xifos, a Virginia Republican organizer. “Brat was always an afterthought to them, even as they spent a lot of money. Central Virginia politics was changing around them and they did not see it.”

Then, some strategists said, Cantor compounded his problems with a blitz of TV ads that attacked Brat, 49. Cantor was apparently intending to bury his underfunded challenger, but the strategy backfired.

“It gave [Brat] oxygen and it gave him sympathy. It was just a tactical mistake,” a Virginia Republican strategist said. “That’s when Brat went from being a guy that die-hard tea party people had heard about to being a guy that just ordinary conservatives driving around and listening to talk radio had heard about.”

Brat only spent $40,000 on the campaign, which would have barely drawn notice had it not been for the million dollars Cantor spent in raising Brat’s profile. Another axiom might have helped Cantor in this regard — never punch down. Had Cantor spent that money on positive retail politicking in his district rather than on an air war against an unknown, the end result may well have looked like McLaughlin’s polling.

What now? Cantor had been the heir apparent to John Boehner, which is one reason why the Tea Party base took aim at him in this primary. Politico runs down the succession to the House GOP leadership, which looks a little more conservative this morning:

Majority Whip Kevin McCarthy, the current No. 3 in the House, is all but certain to run for the majority leader post, GOP sources said. McCarthy’s office declined to comment on Cantor’s loss or McCarthy’s plans.

But the California Republican likely will be challenged by a member of the conservative wing of the House GOP Conference, potentially including Reps. Jeb Hensarling of Texas, Jim Jordan of Ohio or Cathy McMorris Rodgers of Washington.

And a full-scale war will break out for majority whip, with Scalise, McMorris Rodgers and Reps. Pete Roskam (R-Ill.) and Pete Sessions (R-Texas) all possibilities for that post.

Roskam had already started unofficially running for whip, if the job came open. A GOP aide said Rep. Steve Scalise (R-La.) decided to officially seek the whip job after receiving a number of calls Tuesday night from conservatives in the party urging him to run after Cantor lost.

GOP Rep. Paul Ryan is next in line for the Ways and Means Committee gavel and has said he wasn’t running for leadership, a stance he may now have to rethink.

Other leadership hopefuls could also emerge, especially among freshmen or sophomore members, although some of the most visible members those classes are running for Senate, leaving Congress or have other roles at this time. This group includes Reps. Jim Lankford (R-Okla.), who is running for Senate; Cory Gardner (R-Colo.), another Senate hopeful; Tim Griffin (R-Ark.); and Trey Gowdy (R-S.C.), who is chairing the Benghazi select committee.

The final lesson comes from John Fund, who argues that this primary should teach incumbents a very valuable lesson about taking their constituencies for granted:

Many constituents of Eric Cantor felt he had ignored them for years, rarely returning home and often ignoring them on key issues ranging from expanding Medicare prescription-drug benefits to TARP bank bailouts. The frustration boiled over at a May party meeting in his district, where Cantor was booed and his ally was ousted from his post as local party chair by a tea-party insurgent. “He did one thing in Washington and then tried to confuse us as to what he did when he came back to his district,” one Republican primary voter told me. …

Primaries are often criticized for low voter turnout. But they are also expressions of the grassroots sentiments of political parties. The lesson tonight is that establishment candidates ignore their most ardent voters at their peril. As political analyst Stuart Rothenberg put it tonight: “The GOP establishment’s problem isn’t with the Tea Party. It’s with Republican voters.”

That, and don’t trust McLaughlin’s polling — which has a track record that should have Virginia Republicans asking how he got the job at Team Cantor in the first place.