Have Democrats found the issue on which they can break what’s left of Senate traditions and parlay a 50-50 split into partisan domination? It’s far from clear that anything will be enough to move the two recalcitrant members of their caucus — Sens. Joe Manchin, D-W.Va., and Kyrsten Sinema, D-Ariz., — to change their minds about voting to change the chamber’s rules that require a majority of 60 in order to invoke cloture and end filibusters. But if anything will do it, it might be the claim that passing their game-changing federal voting rights bill is the only way to...