Eric Cantor and the giant slayer

Republican leader Eric Cantor (left) is toppled by a little-known college professor, David Brat

The grassroots, anti-establishment forces that had taken down incumbent US Republican senators and handpicked party favourites in recent elections were running out of time to claim a high-profile scalp this year. That all changed on Tuesday night.

In a primary election that was overlooked by most (but not all) analysts, Representative Eric Cantor, the second-highest-ranking Republican in the House of Representatives, fell by more than 10% to a political neophyte, David Brat.

It was the first time in history that an incumbent House majority leader, a position created in 1899, had lost to a primary challenger. Up until now, most speculation about Mr Cantor's future was on whether he would succeed John Boehner as speaker of the House of Representatives.

"The notion that Cantor himself would be knifed before he could knife Boehner occurred to absolutely nobody," writes New York magazine's Jonathan Chait.

The resources available to Mr Cantor dwarfed those of Mr Brat. Over the course of the campaign, Mr Cantor raised $5.44m (£3.24m), while Mr Brat only had $207,000 (£123,000). As the New York Times notes, the Cantor campaign spent nearly as much at steakhouses - $168,637 - as Mr Brat did on his entire race.

The Randolph-Macon College professor wasn't even backed by the big conservative Tea Party groups (although they would be quick to claim credit for his victory).

Conventional wisdom was such that the Washington Post's Tuesday morning story previewing the race said Mr Brat "is expected to fall far short" of beating Mr Cantor, due to "disorganisation and poor funding".

Having missed the potential ground-shaking nature of this primary race, the Washington political establishment is now scrambling to figure out what it all means. Less than 24 hours after the polls closed, one immediate consensus takeaway is that any chance of passing meaningful immigration reform legislation in the foreseeable future is dead.

In the closing days of the election, Mr Brat campaigned hard against Mr Cantor's past support for a foreign "guest-worker" programme and a path to citizenship for undocumented immigrants who enter the US as children.

Eric Cantor (left) was considered a leading candidate to eventually replace Speaker of the House John Boehner

"With Cantor's defeat, you can bet Republicans who so much as hinted at supporting an immigration overhaul are hearing footsteps," writes Tim Murphy of Mother Jones.

"Many Republicans believe Cantor tried to play both sides of the street on the issue," writes the Washington Examiner's Byron York, "on one side working on measures to ease the way for more young illegal immigrants to move into mainstream American society, and on the other assuring fellow Republicans that serious immigration reform would not happen this year."

The New Republic's Brian Beutler cautions that immigration is not the real reason why Mr Cantor lost, however. Other pro-reform Republicans, such as South Carolina Senator Lindsey Graham, cruised through their primaries.

Instead, he writes, Mr Cantor's undoing was his failure to meet the high expectations he set for Republicans in Washington, often sacrificing his hard-right allies as part of his "cunning, but devious brand of politics".

"The lesson of his defeat isn't that immigration reform is particularly poisonous," he says, "but that the right expects its leaders to understand they can't subsume the movement's energy for tactical purposes, then grant it only selective influence over big decisions."

Red State's Erick Erickson agrees that while immigration reform is indeed dead, it was Mr Cantor's personality, governing style and ambition that brought the House leader down.

"Cantor's constituent services moved more toward focusing on running the Republican House majority than his congressional district," he writes. "K Street, the den of Washington lobbyists, became his chief constituency."

He continues:

Cantor lost his race because he was running for speaker of the House of Representatives while his constituents wanted a congressman. The Tea Party and conservatives capitalised on that with built-up distrust over Cantor's other promises and made a convincing case Cantor could not be trusted on immigration either. By trying to be both a Virginia congressman and a worthy successor to the speaker in K-Street's eyes, Cantor made it easy for conservatives to mount an under-the-radar case against him.

A new survey by Public Policy Polling seems to back up this line of thought. In Mr Cantor's district, 70% of Republican registered voters supported immigration reform that increased border security while giving undocumented immigrants a path to citizenship, which is well within the bounds of proposals that had been floated in Washington.

Meanwhile, 49% of Republicans polled disapproved of Mr Cantor's job performance - a dangerous number for an incumbent.

There's a famous saying by former Speaker of the House Tip O'Neill that "all politics is local". In the end, Mr Cantor could be out of a job because he took his home-state constituents for granted.

"Cantor let his guard down by focusing on the intrigues of the Capitol and neglecting the demands of district service, constituent contact and visible fealty to local priorities," writes NPR's Ron Elving. "His weakness in that regard was underlined by his primary campaign's failure to turn out more supporters, or even to make sure absentee votes were recruited and secured."

When it became clear to the Cantor campaign that their candidate was in trouble, they responded by pouring money into the race and attacking Mr Brat as a "liberal college professor". These shots at a hard-core conservative like Mr Brat proved ineffective, and perhaps even preposterous enough to backfire on Mr Cantor.

With Mr Cantor out of the picture, the Republican congressional leadership is left to sort out the pieces - and, according to ABC's Rick Klein, they're in disarray.

"Any thought of the House Republican conference steering back toward a moderate direction in choosing a leader was zapped by Cantor's primary defeat," he writes. "In elevating new leaders, House Republicans seem certain to want to push further to the right now."

Breitbart News's Ben Shapiro says Mr Boehner is a dead man walking as House speaker, and the race to replace him is wide open.

"Boehner's repeated attempts to covertly push amnesty legislation have lost him his base," he writes. "Cantor's ties to Boehner may signal that a successful insurgency is on the way."

Mr Cantor's loss "invites more dramatic action from that clutch of conservatives who have grown increasingly disenchanted with a leadership team that they view as out of touch - demographically, ideologically and strategically", writes the National Journal's Tim Alberta.

In the end, Mr Cantor's story is one more piece of evidence that US politics is becoming increasingly polarised - that carefully crafted congressional districts designed to protect one party or the other are creating circumstances where political primaries, and not general elections, are what make or break candidates.

In the same state, on the same day where a solidly conservative House leader can be defeated by an underfunded insurgent candidate to his political right, Democratic voters less than a hundred miles north nominated a congressional candidate, Don Beyer, who pledged to do everything he can to protect President Barack Obama's health care reforms and pass greater firearm restrictions.

Both Mr Beyer and Mr Brat are considered solid favourites to win in November's congressional elections. They will enter a Congress where compromise is increasingly considered anathema - a betrayal that could be punished by their constituents in the next primary season.