Better question: Does it matter? His defeat’s being received by the powers that be as a referendum on amnesty; no one thinks the prospects for immigration reform are the same as they were 24 hours ago, despite the White House’s lame effort to spin the Graham/Cantor outcomes as a, er, win for reformers. As such, there’s a “Keynesian beauty contest” element to all this. Whatever the real reason is for why Cantor lost, the reason accepted by the crowd on the Hill is immigration. That’s what matters. Wonderful news for border hawks.

But let’s stick with the question, just for funsies. Did amnesty do him in? Some smart observers think there’s more to it than that. Erick Erickson:

Cantor’s constituent services moved more toward focusing on running the Republican House majority than his congressional district. K Street, the den of Washington lobbyists, became his chief constituency. In Virginia a couple of months ago, several residents of Cantor’s district groused that they were going to support Brat because they did not think Cantor was doing his job as a Virginia congressman. Others no longer trusted him.

Cantor and his staff both lost the trust of conservatives and constituents. They broke promises, made bad deals, and left many feeling very, very betrayed. Much of it was because of Cantor’s hubris and the arrogance of his top staffers. He could not be touched and he could not be defeated. He knew it and they knew it. He kept his attention off his district, constituents, and conservatives while he and his staff plotted to get the Speaker’s chair.

A lefty strategist made the same point:

“Was immigration an issue? Yes. Was it the deciding factor to the tune of 11%? Not no, hell no. It’s a fairy tale,” Virginia Democratic strategist Dave “Mudcat” Saunders said. “People talk. And they talk about Eric Cantor. ‘Where is he?’ His constituent services suck. He was never in the district. And when he was in the district and he went out, he had a [security] entourage with him. He was out gallivanting all over the country being a big deal and this is a lesson.”

Dave Brat hammered Cantor on the trail for being an insider too. Casual observers like me only noticed his amnesty rhetoric, but the Wall Street/Main Street divide was a key part of his pitch. He ran a full-spectrum populist campaign, packed with attacks on Cantor for being too chummy with lobbyists and assorted other cronies. In fact, as Ed noted earlier, a PPP poll of voters in Cantor’s district yesterday found overwhelmingly support for comprehensive immigration reform — even among Republicans:

About 72 percent of registered voters in Cantor’s district polled on Tuesday said they either “strongly” or “somewhat” support immigration reform that would secure the borders, block employers from hiring those here illegally, and allow undocumented residents without criminal backgrounds to gain legal status – three key tenets of an overhaul, according to a poll by the left-leaning firm Public Policy Polling and commissioned by the liberal advocacy group Americans United for Change.

Looking just at Republicans in Cantor’s district, the poll found that 70 percent of GOP registered voters would support such a plan, while 27 percent would oppose.

Meanwhile, Cantor was deeply unpopular in his district, the PPP poll found. About 63 percent of those surveyed in his district said they did not approve of the job Cantor has been doing, with 30 percent of registered voters approving. Among Republicans, 43 percent approved of Cantor’s job performance, while 49 percent disapproved, the survey found.

Polling immigration reform is always, shall we say, problematic, but I think you can square PPP’s data with Brat’s win. The majority of local Republicans might mildly support a grand bargain on amnesty, but on hot-button issues like this, it’s the opponents who have the turnout muscle. Same with guns, of course. The public supports expanded background checks overwhelmingly but few House Republicans would dare back it for fear of being swamped by gun-rights enthusiasts at the polls in their district. My theory, then, cliche though it may be, is that Cantor got swept away by a perfect storm. He was too disengaged with his district and had been for years; he employed a poor campaign strategy that ended up inadvertently elevating Brat; he faced soul-deep disgust among voters, especially tea partiers, with the Washington status quo, which the House majority leader inevitably embodies to some extent; and, yes, his chatter about DREAMers triggered conservative outrage at House Republicans’ endless flirtation with amnesty and the deceit they often employ to shield themselves from criticism. Cantor actually tried to sell himself in the primary as some sort of immovable object blocking the path to amnesty, a lie that pro-amnesty fanatic Luis Gutierrez was happy to support in the name of protecting Cantor. I’d like to think righties turned out in droves for Brat for that reason too, to send a message to Boehner, Rubio, and the rest that it’s time to stop farking lying about their intentions on immigration already.

And yet, and yet, if that was all that Cantor was up against, I think it would have been a close race. Brat still might have won but not by double digits. What turned this into a rout, I suspect, was the news over the past few weeks — loudly trumpeted by Drudge, Breitbart, and conservative talk radio — about young illegals from Central America crossing en masse over the Texas border. That was the rocket fuel, I’ll bet, that convinced even casual GOP amnesty skeptics in the district that Cantor’s and Obama’s efforts to legalize DREAMers were acting as a magnet at the border. If I were a voter in the district, I would have taken that news as smoking-gun proof that Brat was right and that sending Cantor back to the House would only make that magnet stronger and bigger. Via Breitbart, here’s Chuck Todd making the same point. That’s what turned this from a momentous upset into the surprise landslide of the century.