Democrats have a Senate problem, and not just in the sense that Republicans currently hold the majority or that the prospect of that changing in 2020 is relatively slim. The problem is that the odds of ever changing it are slimmer than is generally realized. Data for Progress, a progressive think tank and advocacy organization, is trying to raise alarm bells about the issue. In a new memo, co-founder Colin McAuliffe writes that “the Senate is an irredeemable institution” that’s biased 3 percentage points in the GOP’s favor and systematically underweights the interests of nonwhite Americans. Of course, the fact...