In a stunning upset propelled by tea party activists, House Majority Leader Eric Cantor, R-Va., was defeated in Tuesday’s congressional primary, with insurgent David Brat delivering an unpredicted and devastating loss to the second most powerful Republican in the House who has widely been touted as a future speaker.

The race was called shortly after 8 p.m. Eastern by the Associated Press, and Cantor conceded a short time later.

“I know there’s a lot of long faces here tonight,” he said to a stunned crowd of supporters in a Richmond hotel ballroom. “It’s disappointing, sure. But I believe in this country. I believe there’s opportunity around the next corner for all of us.”

Brat’s victory gives the GOP a volatile outlook for the rest of the campaign season, with the party establishment struggling late Tuesday to grapple with the news and some conservatives relishing a surprising win.

“This is an earthquake,” said former Minnesota congressman Vin Weber, a friend of Cantor’s. “No one thought he’d lose.” But Brat, tapping into conservative anger over Cantor’s role in supporting efforts to reform federal immigration laws, found a way to combat Cantor’s significant financial edge.

“Eric Cantor’s loss tonight is an apocalyptic moment for the GOP establishment,” said Brent Bozell, chairman of ForAmerica, a conservative group that targeted Cantor throughout the primary. “The grassroots is in revolt and marching.”

Others had a different take. Longtime Virginia Republican strategist Chris LaCivita said Cantor’s work to build the Republican majority had taken him away from his home district. “He spent days, weeks and months traveling the country, raising money to add to the Republican majority. What can be attributed to Eric in doing so is unquestionable. Unfortunately, it had a price.”

Brat, an economics professor, was not considered a major threat until Tuesday night, simply failing to show up to Washington, D.C,. meetings with powerful conservative agitators last month, citing upcoming finals. He only had $40,000 in the bank at the end of March, according to first quarter filings. Cantor had $2 million.

But there were early signs of trouble. Brat exposed discontent with Cantor in the solidly Republican, suburban Richmond 7th Congressional District by attacking the lawmaker on his votes to raise the debt ceiling and end the government shutdown, as well as his support for some immigration reforms. At a May meeting of Republican activists in the district, Cantor was booed, and an ally he campaigned for was ousted as the local party chairman in favor of a tea party favorite.

A similar revolt in the state Republican committee last year determined that the party would hold a two-day convention rather than an open primary to elect candidates in 2013. That decision helped gubernatorial contender Ken Cuccinelli, a conservative hero who lost to Democrat Terry McAuliffe. Many establishment Republicans in the state believe Cuccinelli’s nomination cost them the governorship. The 7th District fight is a sign that the factions in the party have yet to unite.

But a GOP strategist who requested anonymity to speak candidly cautioned against viewing Cantor’s loss as a win for the tea party.

“This is what happens when you don’t tend the weeds in your backyard,” the strategist said. he went on to question Cantor’s decision to go up on television — a strategy that may have raised Brat’s profile and let more voters know about the race. “Six weeks ago, Brat was an unknown. The question will be: Did the campaign overreact?”

A seemingly critical issue for Cantor was immigration. The majority leader had championed a Republican version of the Dream Act, which would enable some undocumented immigrants who entered the country as children to qualify for in-state college tuition rates. Although Cantor never brought the legislation to the House floor, his support for the idea irritated staunch opponents of immigration reform.

The strategist also noted that Republicans will study Tuesday’s results carefully for signs of Democratic crossover, but anecdotally, he did not hear that was a real issue. “People always talk about that, but it hasn’t ever materialized.”

Since his days in the Virginia legislature, Cantor has been on the side of the pro-business establishment. But he began to forge ties with the tea party in 2010, positioning himself as a conservative counterweight to House Speaker John Boehner, R-Ohio, after the movement helped sweep Republicans into power. Yet tea party activists in his own district have never embraced him.

Cantor had taken the primary threat seriously, attacking Brat in television ads and boasting in mailers that he blocked “amnesty” for illegal immigrants on Capitol Hill.

Cantor addressed the crowd for about four minutes, thanking supporters and saying he would continue to “fight for the conservative cause.”

Cantor quickly exited the ballroom for a waiting SUV, ignoring questions from reporters.

But to add to the drama of the evening, after Cantor left, immigration activists stormed the ballroom, screaming and waving a flag. “What do we want? Immigration reform! When do we want it? Now!”

A Spanish-speaking hotel employee took the microphone Cantor had used and told the protesters in Spanish that the police were on their way.

The winner of the GOP primary will face Democratic Party nominee Jack Trammell — a professor at Randolph-Macon College, the same school where Brat works — in the general election this fall.