House Majority Leader Eric Cantor fell to challenger Dave Brat on Tuesday in a stunning primary upset likely to send shockwaves through Congress and the Republican Party.

The Associated Press called the race for Brat shortly after 8 p.m. Eastern time — marking the first defeat ever of a sitting House majority leader.

"Obviously, we came up short," Cantor conceded to supporters, with his wife, Diana, by his side, shortly after the result was called.

"It's disappointing, sure," Cantor added. "But I believe in this country. I believe there's opportunity around the next corner for all of us."

The result will no doubt cause a leadership scramble on the Hill, where Cantor was expected by many within the Republican Party to one day succeed House Speaker John Boehner. It was not immediately known whether Cantor planned to remain as majority leader for the duration of his term, nor whether he plans to wage a write-in campaign for re-election. A spokesperson did not respond to a request for comment.

“Eric Cantor and I have been through a lot together,” Boehner said in a statement. “He’s a good friend and a great leader, and someone I’ve come to rely upon on a daily basis as we make the tough choices that come with governing.”

Cantor's campaign knew a challenge from the right flank could be serious and did not take the match-up with Brat for granted, spending close to $1 million on the second-ranking House Republican's re-election bid. Brat's campaign spending, meanwhile, was in the low six-figures.

Cantor also made a last-minute push for his seat with a slew of new advertisements, including a positive ad touting Cantor as an adversary to President Obama, and another attacking Brat as a "liberal college professor."

Cantor appeared in a strong position heading into the election Tuesday. An internal poll released days ago by his campaign showed Cantor leading Brat by a whopping 34 points; and, as recently as last week, top Cantor political adviser John Murray expressed confidence in private conversations that Cantor would win by nearly that margin.

However, Cantor’s re-election strategy had key fatal flaws. Despite serious spending and encouraging polling, he lost to Brat by a wide margin, more than 10 points.

In television ads airing as early as April, Cantor’s campaign attacked Brat by name, likely increasing his name identification for voters looking for an alternative to Cantor.

Cantor might also have suffered at the polls in part due to the more conservative make-up of his district in this election cycle compared to the last. Congressional redistricting redrew Virginia's 7th District to encompass more dark-red Republican territory, eliminating a share of Cantor's moderate-Republican core.

And the polling for Cantor’s campaign proved to be well off base.

“He wasn't caught off-guard,” said one Republican operative. “He just flat-out lost.”

In buoyant statements from Democrats and conservative Republicans alike, Cantor’s loss was framed as proof-positive that voters are fed up with Republican incumbents in Washington.

“Eric Cantor is the personification of frustration with Washington, and House Republicans should be terrified of the backlash from the voters who have been alienated by their race to the right,” said Rep. Steve Israel, D-N.Y., chairman of the Democratic Congressional Campaign Committee.

Tea Party groups, which were not active in boosting Brat against Cantor, echoed that rationale -- but pointed to Cantor's support for some manner of immigration reform as his fatal mistake.

“Dave Brat won tonight in Virginia because he effectively harnessed the outrage at Washington over the policies that have not been representative of the people, including the prospect of amnesty for illegal immigrants, and focused it on one political leader — the Republican who’s been pushing for amnesty harder than anyone else in the House GOP Leadership,” said Jenny Beth Martin, chairwoman of Tea Party Patriots.

Indeed, Cantor has grappled with finding a middle ground on immigration reform. He rejected the Senate’s plan outright, but expressed hope, as did Boehner and other House Republican leaders, that a House version of reform could at some point come to fruition.

Cantor’s rhetoric on that issue might have hit too cooperative a tone for his party’s primary voters, however. In a recent interview, Cantor even mentioned his willingness to work with Obama to find a solution.

“I have told the president, there are some things that we can work on together,” Cantor said in the interview, which aired on a local news station in Virginia. “We could work on the border security bill together, we could work on something like the kids. But so far the president has insisted it’s all or nothing, my way or the highway, and that’s just not going to happen.”

Cantor arrived in Congress in 2001, having served previously in the Virginia House of Delegates, and rose quickly, culminating in his election to the role of leader when Republicans took the majority in 2011. He is the highest-ranking Jewish elected official in the country.