In 2016, everyone thinks the Senate “map” is terrible for Democrats. Forty-two Republican incumbents don’t face an election this year, whereas Democrats must defend 24 incumbents, 10 of them in states that Donald Trump won in 2016–sometimes by very large margins. Even a Blue Wave is expected to leave the Republicans in charge of the Senate.

You would think that 2020 would have to be better for Democrats. After all, Democratic voters outnumber Republicans in national votes for the president and the House. If, by the luck of the draw, the Democrats face a bad Senate map one year, the next time has to be better–right?

Actually, 2020 looks like another pretty hard year for the Dems. According to Nathaniel Rakich in FiveThirtyEight, 22 Republican Senators will face reelection. That sounds like fertile ground for Democrats, except that only two of those 22, Cory Gardner and Susan Collins, represent states that Hillary Clinton won in 2016. Based on that information, you might expect Republicans to lose just a seat or two. Meanwhile, 11 Democratic Senators will face reelection, and two of them represent states that Trump won in 2016: Jeanne Shaheen of New Hampshire (which was close) and Doug Jones of Alabama (which Trump won by 27 points). Based on that information, you might expect the Democrats to lose Jones and maybe one or two more.  If each party loses a seat or two to the other, it will be a wash, preserving the Republican majority.

How can this be? One reason is that a harder year will finally arrive for the Republicans in 2022. Twelve Democrats and 22 Republicans will have to defend seats that year, including several Republicans in swing states: Rubio in Florida, Grassley in Iowa (if he runs again at 89), Burr in North Carolina, Portman in Ohio, Toomey in Pennsylvania, and Johnson in Wisconsin. All the Dems who are up in 2022 are in either blue or purple states.

But the other reason is the extraordinary gap between the Senate and the American population. Even now, with the Senate controlled by Republicans, Democratic senators represent substantially more people:

The Constitution enshrines this imbalance. Anything in the whole document can be changed by amendment, “provided that… no state, without its consent, shall be deprived of its equal suffrage in the Senate.” This is is our only unamendable rule.

Long-term predictions are foolish, but I think you can imagine a pattern of Democratic presidents and House majorities being systematically stymied by Republican senates and the Supreme Court that the Senate has shaped. Then a significant majority of the public will be consistently blocked by an increasingly radicalized minority that is based in different parts of the country as we address climate crises, AI, and other truly profound challenges. Many people will not trace the failures of the government to specific provisions in our Constitution; they will perceive a government that’s inexplicably unresponsive and unrepresentative. And that, it seems to me, is a recipe for constitutional collapse.

See also: is our constitutional order doomed?; two perspectives on our political paralysis; and are we seeing the fatal flaw of a presidential constitution?