Senate Democrats are in a bind. Sen. Dianne Feinstein of California is on an extended medical absence due to a case of shingles, depriving Democrats of their majority on the Judiciary Committee. There is no way of knowing when, or even if, the octogenarian will return, and recent efforts to replace her plum committee seat have failed. She could resign of her own accord, and she’d swiftly be replaced by a senator able to perform his or her duties, but she’s so far refused to bow to such pressure. That effectively robs Democrats of their ability to easily advance federal judges for confirmation — which is one of the few things the party can do without control of the House. Feinstein’s been in office for a long time, even by senatorial standards. And recent reports have detailed her colleagues’ and former staff members’ doubts regarding her cognitive function. Plenty of older men have remained in their seats as they battled debilitating illnesses like cancer, or following a stroke. But...