In a House race, where many voters are unfamiliar with challengers until the very end, it’s not nearly as instructive to look at who’s winning as it is to see whether the incumbent is winning a majority of the vote. Traditionally, most of the undecided vote breaks toward the challenger — especially in a wave election. It’s not uncommon for a congressman to be up “double digits” but still be in serious trouble, given the anonymity of the opponent.

And a staggeringly high number of Democratic incumbents are below the 50 percent mark, including members in much of the polling conducted by Democratic firms released to counteract the GOP narrative. House Race Hotline editor Tim Sahd compiled an invaluable database of all the House race polling conducted this cycle and found 66 Democratic incumbents sitting below that magic 50 percent number.

That number should send shivers down the spines of Democratic strategists. In 2008, when Democrats coasted to victory across the board, 32 House Republican incumbents were under the 50 percent mark in the last poll of the cycle, and 14 of them lost — a 44 percent mortality rate. When you account for all the vulnerable open seats and the competitive races where polling hasn’t yet been released, it’s very hard to see how Democrats can hold their majority.