There were signs that Eric Cantor was in trouble, but even in retrospect they were subtle.

In April, Cantor's campaign had begun to attack his challenger, Dave Brat, by name, lending credibility and name recognition to a largely unknown, untested candidate.

Then, in May, a key Cantor ally, Linwood Cobb, fell in a convention to a more conservative opponent for the role of the party’s 7th District chair — an outcome Cantor’s network actively worked to prevent. At the convention, conservative activists booed Cantor.

Still, few could have read those tea leaves to predict that Cantor, the House majority leader and a prohibitive favorite to win re-election, would fall Tuesday to a college professor with an amateur political operation, zero experience as an elected official, and no support of consequence from Tea Party groups.

Brat trounced Cantor by 12 points — shocking the Republican Party to its core and lending renewed purpose to Tea Party groups that had been losing steam.

Some of those groups, including Tea Party Patriots and Freedomworks, jumped to laud Brat on Tuesday after he clinched the race, although they had not supported him financially or otherwise during the contest.

“This victory is a referendum on the establishment that has gone along with policies that have completely left out the voice of the people,” said TPP chairwoman Jenny Beth Martin. “This is the people’s house and we are reclaiming it for the people.”

With more than half of this season's primaries already complete, however, the effects might be felt only in isolated spots on the campaign trail, if at all. Chris McDaniel, an upstart conservative challenging Sen. Thad Cochran, R-Miss., might reap rewards in two weeks in a run-off election; and other insurgents with long odds have latched on to the news, hoping for a boost.

"What we have seen ... in Virginia shows that no race should be taken for granted and all the money and position in the world doesn't resonate with an electorate that is fed up with a Washington establishment that has abandoned conservative principles,” said Joe Carr, who is taking on Sen. Lamar Alexander, R-Tenn., in a primary.

There could be myriad implications, potentially grave, for a Republican Party that was believed to have found its footing against insurgent candidates and groups this election cycle, after stumbling in 2012.

In the immediate aftermath of Cantor’s defeat, shocked Democrats were hopeful that might be the case.

“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.

Privately, however, Democrats and some Republicans worried that Cantor's stunning loss could be taken as a referendum on his immigration-reform stance: He opposed the Senate's plan but, like Speaker John Boehner, has called for some measure of reform in the House -- and even tried to work with President Obama on the issue.

“I have told the president, there are some things that we can work on together,” Cantor said of immigration reform in a recent interview with a Virginia news station. “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.”

But early evidence suggests a fraught campaign, not Cantor’s stance on any particular issue, might be most to blame — meaning the lesson Republican candidates draw from this race could be the most obvious: strong campaigns win elections.

Cantor did not take his challenger for granted. He attacked Brat early, and Cantor outspent him 10-to-one. But Cantor’s team appears to have misjudged at the district convention last month.

The campaign was also gravely off base in its internal polling, which days before the election showed Cantor leading Brat by 34 points. Cantor’s team was so confident he would win that an adviser, John Murray, said in private that Cantor would hit 60 points; on the morning of Election Day, Cantor was reportedly in D.C., not in his district.

“You can't see a primary coming, prepare for it and spend a sufficient amount of money on it, and not be blamed for the loss,” said one Republican operative with House campaign experience. “That's a bad strategy and bad polling, period, full stop.”