E.J. Dionne Jr., Norman J. Ornstein and Thomas E. Mann are the authors of "One Nation After Trump: A Guide for the Perplexed, the Disillusioned, the Desperate, and the Not-Yet-Deported," from which parts of this article are drawn.

Why does our political system make it impossible even to consider solutions to gun violence? After the massacre in Las Vegas that has so far taken nearly 60 lives and left more than 500 injured, the first reaction of the many politicians who carry water for the gun lobby was to declare it "premature" to discuss measures to keep guns out of the wrong hands.

The "premature" word echoed from President Trump's White House on down, and those who used it were really saying that Congress would never enact even modest efforts to prevent mass shootings. This is damning evidence of the stranglehold that far-right lobbies have on today's Republicans, who extol law and order except when maintaining it requires confronting the National Rifle Association.

But something else is at work here. As we argue in our book, "One Nation After Trump," the United States is now a non-majoritarian democracy. If that sounds like a contradiction in terms, that's because it is. Claims that our republic is democratic are undermined by a system that vastly overrepresents the interests of rural areas and small states. This leaves the large share of Americans in metropolitan areas with limited influence over national policy. Nowhere is the imbalance more dramatic or destructive than on the issue of gun control.

Our fellow citizens overwhelmingly reject the idea that we should do nothing and let the killings continue. Majorities in both parties favor universal background checks, a ban on assault-style weapons, and measures to prevent the mentally ill and those on no-fly lists from buying guns.

Yet nothing happens.

The non-majoritarian nature of our institutions was brought home in 2013. After the Sandy Hook slaughter, the Senate voted 54 to 46 in favor of a background-­checks amendment crafted by Sens. Joe Manchin (D-W.Va.) and Pat Toomey (R-Pa.). Those 54 votes were not enough to overcome a filibuster, which the GOP regularly abused during the Obama years. Worse, since most large-state senators voted for Manchin- ­Toomey, the 54 "yes" votes came from lawmakers representing 63 percent of the population. Their will was foiled by those who speak for just 37 percent of us.

Ending the filibuster would not solve the problem; in some cases, it might aggravate it. As The Post's Philip Bump has noted, if all 50 senators from the 25 smallest states voted for a bill and Vice President Pence cast his lot with them, senators representing just 16 percent of Americans could overrule those representing 84 percent.

And this problem will only deepen. David Birdsell, a Baruch College political scientist, has calculated that by 2040, 70 percent of Americans will live in 15 states — and be represented by only 30 of the 100 senators.

In the House, mischievously drawn district lines vastly distort the preferences of those who cast ballots. After the 2010 Census, the GOP controlled the redrawing of congressional boundaries in most key states. The result? The Brennan Center for Justice concluded that Republicans derived a net benefit of at least 16 seats from biased boundaries, about two-thirds of their current House margin.

The electoral college, meanwhile, is increasingly out of line with the popular vote. In raw terms, Trump had the largest popular-vote deficit of any electoral college winner. It was the second time in just five elections that the two were at odds. Here again, the failure of our institutions to account for the movement to metropolitan areas is the culprit. In 1960, 63 percent of Americans lived in metros; by 2010, 84 percent did.

Voter-suppression efforts and the disenfranchisement of former felons in many states further skew electoral outcomes, as does the power of money in politics.

Constitutionally, representation in the Senate is difficult to change. But this week, the Supreme Court heard a case on which it could (and should) rule to make gerrymandering much harder. A renewed Voting Rights Act and universal voter registration could restore access to the ballot box to those who have lost it. The National Popular Vote Interstate Compact is trying to move us toward the popular election of the president. And our campaign finance system badly needs repair.

Our paralysis on guns reflects a looming legitimacy crisis in our system. In the short run, advocates of sane gun laws should keep up the pressure, particularly in election showdowns involving candidates who resist any steps to make our country safer. In the long run, we need reforms to make majority rule a reality.

E.J. Dionne Jr., Norman J. Ornstein and Thomas E. Mann are the authors of "One Nation After Trump: A Guide for the Perplexed, the Disillusioned, the Desperate, and the Not-Yet-Deported," from which parts of this article are drawn.