In his book “The American Mind,” from 1950, which I took down from the bookshelf during the weekend, the historian Henry Steele Commager notes that “the American” of the late nineteenth century had “little time for tradition and authority,” because “he knew that his country had become great by flouting both.” Simultaneously, however, the American “thought his government and the Constitution the best in the world, credited them with a large measure of the success of his experiment, and would not tolerate any attack upon their integrity.” Although some of Commager’s language, such as the use of “he,” grates on the modern ear, the paradox that he identifies survives to this moment, and it is doing untold harm to this country. The horrible events of the past few days have confirmed that the United States, while it remains a great nation, is a country trapped by its past. Despite a rising tide of gun violence and political extremism, it has repeatedly failed to adapt its institutions and its laws—particularly those relating to guns and the online spread of hate speech—to an age of technology-enabled savagery. Now the very foundations of the political system that so many Americans take for granted seem to be under threat.

Is that a bit alarmist? On the basis of what we know, Robert Bowers, the forty-six-year-old loner who carried out a massacre at a synagogue in Pittsburgh on Saturday, and Cesar Sayoc, Jr., the former male stripper from Florida who has been charged with sending mail bombs to opponents of President Donald Trump, are both alienated people who have lived small lives filled with resentments and failures. Nonetheless, the larger threat that their acts of terror represent shouldn’t be understated. When opposition politicians cannot open their mail without fear of being blown up, when people of religion cannot attend their houses of worship without fear of being shot to death, and when the President cannot forswear partisan attacks for more than a few hours after a deadly act of terror, then liberal democracy is malfunctioning in tragic fashion. As Americans, and particularly Jewish Americans, watched the news this weekend, they could be forgiven for believing that the horrors other countries have endured at other times were now upon them.

Of course, a few isolated acts of political violence do not add up to a conflagration. But the pluralist American model badly needs shoring up, and some of the necessary measures are obvious ones. The United States needs new gun laws that make it impossible for anyone full of hate to accumulate a personal armory. It needs restraints on the propagation of hate speech that take account of the fearsome reach and power of the Internet. It needs changes to the electoral system that empower the will of the majority, while still affording protections for minorities. And the country needs a President who isn’t an arsonist.

If some of these reforms involve making significant alterations to the system of government that the Founders created, which is still accorded the same level of veneration in some quarters that it was in Commager’s day, so be it. When James Madison proposed the Second Amendment, he wasn’t living in a world where isolated haters could convene online and convince themselves that they were engaged in an apocalyptic struggle much larger than the daily drudgery of their lives. (“I can't sit by and watch my people get slaughtered,” Bowers wrote in his final social-media post. “Screw your optics, I’m going in.”) The founders didn’t inhabit an environment where deadly weapons of war, such as rifles that can fire dozens of rounds a minute, are mass-produced for private use, and where bomb-making plans are freely available on the Internet. (According to news reports, Bowers owned more than twenty weapons, including the AR-15 rifle he used at the Tree of Life synagogue.)

And, of course, the Founders, who worried greatly about the vulnerability of democracy to populist demagogues, didn’t envision a President like Trump. Doubtless, the anger and hatred that motivated Sayoc, who reportedly lived in a white van outside a strip mall, was rooted in some personal humiliations or privations he suffered long ago. But he wore a MAGA hat and directed his venom at individuals whom Trump had targeted in his speeches and Twitter posts. To deny that there is any link between the President’s rhetoric and such acts, as Vice-President Mike Pence did on Sunday, is to engage in Trump-level deception; to insist that there is no link between gun violence and gun laws, as the G.O.P. has done for decades, is to engage in the same deception.

Commager pointed out that his naïve subjects had some grounds for believing they were the beneficiaries of divine provenance. “Nothing in all history had ever succeeded like America, and every American knew it,” Commager wrote. “Progress was not, to him, a philosophical idea but a commonplace of experience: he saw it daily in the transformation of wilderness into farmland; in the growth of villages into cities; in the steady rise of community and nation to wealth and power.”

The descendants of Commager’s Americans have no excuse for being complacent. While the United States remains an economic leader, it appears right now to be spiralling into a miasma of acrimony, post-truth thinking, and violence. The combination of ubiquitous connectivity, unregulated social media, lax gun laws, and rampant political demagoguery is presenting a challenge that our system of government hasn’t faced before. To be sure, the issue of whether the center will hold isn’t exclusive to the United States. Sunday’s election result in Brazil and the announcement by the German Chancellor, Angela Merkel, on Monday, that she won’t run for office again both testified to the fact that liberal democracy is facing a global challenge. But the United States is a special case. At least until Trump entered the Oval Office, the country liked to view itself as a model for others to follow, and, indeed, it did play such a role, however imperfectly.

Can the country summon the desire to aspire again and the internal will to fortify the values on which its aspirations were based? Next week’s midterm elections will provide a timely and crucial opportunity to answer in the affirmative. Let’s hope and pray that it isn’t spurned.