Tea party activists attend a rally on the grounds of the Capitol in Washington. (J. Scott Applewhite/Associated Press)

Since its inception five years ago, the tea party's biggest calling card has been knocking off incumbent Republicans. Sen. Lamar Alexander's (R-Tenn.) win Thursday means that, for the first time since the movement launched, it failed to knock off a single incumbent Republican senator.

But Alexander's relatively close shave — he leads Joe Carr 49.7 percent to 40.5 percent with some votes still being counted — also belies this truth about the 2014 election: The establishment won, but it wasn't easy.

In fact, of the 12 GOP Senate incumbents seeking reelection this year, one-quarter of them took less than 50 percent of the vote in their primaries: Alexander, Pat Roberts (R-Kan.) and Thad Cochran (R-Miss.). (Cochran later cleared 50 percent in his primary runoff with Chris McDaniel ... when he took 51 percent.)

In addition, three other GOP senators took 60 percent or less of the vote: Lindsey Graham (R-S.C.), John Cornyn (R-Tex.) and Mitch McConnell (R-Ky.).

None of these latter trio of senators were in real danger on primary day, but it's still very rare for an incumbent to take 60 percent of the vote or less. In fact, as I noted a few months ago, historically less than 5 percent of Congress fails to clear 60 percent in their primaries. For GOP Senate incumbents this year, it was 50 percent.


(Caveats: There is still one non-competitive incumbent primary left: Wyoming Sen. Mike Enzi. And McConnell technically took 60.2 percent of the vote, but for the purposes of this exercise, we're rounding him to 60 percent.)

The six men listed above have served a combined 120 years in the Senate, and basically none of them has faced a serious primary challenge as an incumbent. They all won, and most did so relatively comfortably — which has got to be hugely encouraging for Republican establishment efforts to beat back the increasingly antagonistic tea party.

But to suggest the tea party didn't get any traction this primary season would be a gross oversimplification.