The Republican coalition of rural whites, exurban whites and anti-tax suburbanites may not be large enough to win the national popular vote in a head-to-head matchup with Democrats. But it covers a much larger part of the country’s landmass, giving it a powerful advantage in the Senate. And while this coalition — or its Democratic counterpart of liberal whites and the overwhelming majority of nonwhites — isn’t set in stone, it could be years, even decades, before we see meaningful change in the demographic contours of our partisan divides.

Politics is unpredictable and events matter, but it’s also clear that Republicans are on the verge of a durable structural advantage in the Senate that will make Democratic majorities rare outside of the occasional “wave” election.

There are no immediate solutions to this problem. But progressives — who have the most to lose if the Senate becomes an even larger obstacle to their preferred policies — have started to brainstorm about reforms that might make the Senate more democratic and representative without changing the Constitution itself.

One path involves statehood. In his book “It’s Time to Fight Dirty: How Democrats Can Build a Lasting Majority,” David Faris, a political scientist at Roosevelt University in Chicago, calls for at least eight new states. The first is Washington, D.C. The second is Puerto Rico, assuming its inhabitants agree to statehood. And the next six would be formed from America’s superstate, California. “If the state were more or less evenly divided between left and right, its comparative lack of power in the federal government would be less of an issue,” Faris writes. “But California is now one of a handful of the most left-leaning states in the entire union, and Californians’ lack of voting power and Senate representation means that the country is pulled inexorably to the right.”

It’s a radical solution, and while it might work, it has one clear downside — Republicans could respond in kind with similar schemes for conservative megastates like Texas and, to a lesser degree, Florida. And that’s assuming California voters would sign on to the project. But finding ways to expand the Senate with new members is the right idea, and a recent report from the Roosevelt Institute, a progressive think tank, offers an approach that doesn’t rely on extreme forms of constitutional hardball.

To accommodate the demographic trends of the next few decades, the institute calls for expanding the Senate to include other federal units besides states, for the sake of greater democracy and representation: “A modern Senate should reflect a modern federalism encompassing not only states and the federal government but also the district, territories and tribes.”

Under the Roosevelt Institute proposal, Washington, D.C., the Atlantic territories, the Pacific territories and the Native tribes would each receive two senators and a voting member in the House of Representatives. Individual units could still pursue statehood, but the lack of that recognition wouldn’t preclude representation in Congress.