​Bob Schieffer on a number to fear

House Majority Leader Eric Cantor, R-Va., delivers his concession speech as his wife, Diana, listens in Richmond, Va., Tuesday, June 10, 2014. Cantor lost in the GOP primary tp tea party candidate Dave Brat.

AP/Steve Helber

The political world was stunned last week when little-known college professor David Brat beat House Majority Leader Eric Cantor, but Brat knew exactly why it happened.

"This is a miracle from God that this happened," he said.

Who am I to say he's wrong?

But here's my question: Whether or not it was a miracle, why do Congressional leaders get beat in years that end in 4?

It was in 1994 that revered, long-time House Speaker Tom Foley got beat by a Republican thought early on to have no chance.

It was in 2004 that popular Senate Majority Leader Tom Daschle lost his seat in a stunning upset.

And now, right on schedule 10 years later in 2014, the folks back home took down Eric Cantor, number two in the House Republican leadership, and the odds-on favorite to be the next House Speaker.

Every parent knows about the "terrible twos," but if I held a Congressional leadership post, what I'd worry about are "the fearsome fours."

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    Bob Schieffer is a CBS News political contributor and former anchor of "Face The Nation," which he moderated for 24 years before retiring in 2015.