Eric Cantor after news conference
U.S. House Majority Leader Eric Cantor (R-VA) leaves after a news conference at the U.S. Capitol in Washington June 11, 2014. REUTERS/Yuri Gripas

As the political world on Wednesday absorbed the stunning defeat of House Majority Leader Eric Cantor, many incumbent Republicans divined an uncomfortable message: No matter how conservative their credentials and regardless of the size of their campaign war chests, they could yet find themselves branded part of the establishment and defeated by a Tea Party insurgent.

Not long ago, conventional wisdom had it that the Tea Party was effectively a spent force, a populist surge that had elevated individual candidates in uniquely conservative districts while damaging the Republican party nationally by taking it to extremes not palatable to the American mainstream.

But with the wholly unexpected defeat of Cantor, a seven-term Republican who had been seen as a likely candidate to become Speaker in the next Congress, all eyes turned to other races in which well-financed Republican incumbents are fighting off Tea Party challengers -- not least, to Mississippi, Kansas and Tennessee.

“Because it was so unexpected, that’s a lot scarier to incumbent members of Congress,” Ron Rapoport, John Marshall Professor of Government at the College of William and Mary in Virginia, told International Business Times. “Politicians like predictability and this election showed there may not be as much as they’d like to think.”

In Mississippi, for example, Sen. Thad Cochran is a nearly-40-year incumbent perceived as moderately conservative: the kind of Republican who in times past would've been pretty much safe for life. Today? He's in a tight race with Tea Party challenger and state legislator Chris McDaniel. The state’s primary election takes place later this month, and the most recent polling shows McDaniel with a 3 percent lead. Sarah Palin visited Mississippi to endorse McDaniel and has recorded robocalls on his behalf.

“Chris McDaniel is not someone to be taken lightly,” Brandon Jones, executive director of Mississippi Democratic Trust, told IBTimes. “The Tea Party has never truly gone away since 2010. The challenge for folks of the Republican establishment is to put a candidate up who can satisfy those voters.”

Kansas Sen. Pat Roberts also finds himself with a Tea Party challenger, Milton Wolf, who held up the example of David Brat's win over Cantor to warn other Republicans of their vulnerability.

“Eric Cantor isn't the only incumbent from Virginia who is going to lose his primary this year,” Wolf said in a statement to reporters, alluding to a controversy over Roberts’ residency, after disclosures that he has lived in suburban D.C. for decades. “On August 5th, it’s Pat Roberts' turn.”

Facing a primary in August, Tennessee Sen. Lamar Alexander has the same weaknesses that Cantor did. He's got a low approval rating at home, and he's been pegged by his Tea Party opponent -- State Rep. Joe Carr -- as a supporter of immigration reform (or "amnesty," in the rightwing's lethal lexicon). Carr congratulated Brat on Tuesday. “What we have seen tonight in Virginia shows that no race should be taken for granted," Carr said, according to "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.”