As a recent series of court decisions in Pennsylvania have brought to national attention, Republicans are able to achieve this amplification of their popular support by taking advantage of the tendency of Democrats to cluster in densely populated urban areas and combining it with state laws that permit the party holding power at the state level to set the boundaries of congressional districts. The result in Pennsylvania has been an egregiously unfair partisan skew — with Republicans in 2016 slightly losing the statewide popular vote and yet winning 72 percent (13 out of 18) of the state’s congressional districts. (In neighboring New Jersey, where redistricting is handled by an appointed commission, a statewide popular vote outcome favoring the Democrats 54 percent to 46 percent yielded a much fairer congressional delegation of seven Democrats and five Republicans.)

Pennsylvania might push the tactic further than most states, but enough of them engage in similar practices that to win control of the House, Democrats need to do much better than prevail with just over 50 percent of the nationwide vote. To be assured that they win a majority, Democrats likely need to trounce Republicans by at least 7 to 10 percentage points.

That’s incredibly galling — a blatant injustice at the core of our democracy that’s impossible to justify as anything other than an attempt by Republicans to rig the system in their own favor. And that’s how the GOP may well have set up the conditions of its own undoing.