There it was: 39 percent. Floor broke. Threshold crossed. The close of Barack Obama’s awful week. One more awful August. On Sunday, for the first time in his presidency, Obama’s public approval rating dipped below 40 percent in the Gallup Poll.

Now polls are like life. The older one gets, the less remarkable the ebbs and flows become. Or the longer the trend line, the smaller the blips seem. But some poll numbers capture more. Gallup has an innate symbolism. As gold standards do. And 39 percent is emblematic of that oldest incumbent problem: selling hard times.