In one of his first public speeches, in early 1838, Abraham Lincoln warned that the biggest threat to the United States came from within. “If destruction be our lot,” said the future president, then 28, “we must ourselves be its author and finisher. As a nation of freemen, we must live through all time, or die by suicide.”

Citing the killings of a mixed-race boatman and an abolitionist newspaper editor by pro-slavery crowds, Lincoln described a country in which widening political division had turned into violence, declaring:

There is, even now, something of ill-omen, amongst us. I mean the increasing disregard for law which pervades the country; the growing disposition to substitute the wild and furious passions, in lieu of the sober judgment of Courts; and the worse than savage mobs, for the executive ministers of justice … By instances of the perpetrators of such acts going unpunished, the lawless in spirit, are encouraged to become lawless in practice; and having been used to no restraint, but dread of punishment, they thus become, absolutely unrestrained.

The same lack of restraint is evident in today’s runaway partisanship. As the coronavirus spread in the United States, former President Donald Trump downplayed the danger, and many of his supporters came to view recommended health precautions through a political lens, exacerbating terribly the pandemic’s consequences. Trump managed to turn purely factual questions, such as which candidate had won the 2020 presidential election, into matters of bitter partisan dispute. After Trump’s support for a violent mob of insurrectionists who attacked the Capitol on January 6 triggered his impeachment, many of my fellow Republicans preferred to punish not the president but those in the party, including Representative Liz Cheney and Senator Mitt Romney, who wanted to hold him accountable.

As many others have pointed out, Trump is as much symptom as cause of this corrosive version of partisanship. Although partisan intolerance predated him—think of how Republicans denied Merrick Garland a confirmation vote for a Supreme Court seat in 2016—elected officials evidently believe he represents the views of their voters.

The internal divisions now on display have become the most serious threat to American security. Foreign enemies such as Russia and China can and do try to weaken us through subversion of our civil society. Those efforts showed some effectiveness in the 2016 election. They were largely irrelevant in 2020, partly because the U.S. put up better defenses but also because Americans were already deeply divided even without foreign intervention. That is, even though Americans have the means to protect ourselves from outside efforts to inflame partisan passions, we are doing to ourselves what our country’s enemies would have done.

Our current level of partisanship is destabilizing in more prosaic ways. It makes legislative endorsements of treaties and other foreign-policy instruments rare, so presidents instead pursue their goals by executive order. And they can overturn executive orders issued by their predecessors, as Trump did when dropping out of the Paris Agreement and the Iran nuclear deal. Countries that wish to strike trade deals, agree to arms-control measures, or commit forces to fight alongside us do not know if a future president will unilaterally reverse course. If there are no enduring commitments with the U.S., any deal is risky for our foreign counterparts.

More and more, America’s alliances are becoming grist for partisan politics. Israel is the bellwether, given the ferocity of Prime Minister Benjamin Netanyahu’s support for the previous administration, but public support even for NATO allies is now colored strongly by party affiliation. Republican backing for the alliance dropped early in the Trump years and has not fully recovered.

Partisanship also diminishes U.S. soft power—the magnetism of our example—which is such an important part of why the U.S. is the global hegemon and why the cost of remaining so has been sustainable for decades. Other countries want us to succeed, want to partner with us, because of what we represent. And that has been badly damaged by the Trump years.

How might Americans overcome these dynamics, so that we do not become the author and finisher of our own destruction?

England in the 18th century experienced similarly deep polarization over religion. Edmund Burke advocated relaxing anti-Catholic restrictions on the basis that “the people would grow reconciled to toleration, when they should find by the effects, that justice was not so irreconcilable an enemy to convenience as they had imagined.” That is, government builds tolerance when it solves problems.

President Joe Biden clearly takes that as his operating premise, contrasting a competent administration’s national pandemic response with the operatically ineffectual chaos of his predecessor. Boring competence may well come back into fashion.

Franklin D. Roosevelt’s experience early in his presidency suggests that active government efforts needn’t even solve problems to affect public attitudes. By promising a flurry of activity during his first 100 days in office, Roosevelt convinced Americans that the new president was trying to solve the country’s urgent problems. That didn’t diminish partisanship (recall the jubilation with which Roosevelt said of his critics, “I welcome their hatred”), but it did expand public support for his efforts.

Structural changes to our political system could attenuate partisanship. Among them are ranked-choice voting, nonpartisan primaries, and a reduction in gerrymandering by removing congressional redistricting from partisan control. Reassessing the role of media and social-media companies will also be important in reducing polarization. Facebook, Twitter, and others have sped the transmission of information and broadened the reach of individual voices, but have also facilitated isolation from objective facts. Figuring out how to defang talk-radio and cable-news propagandists in a manner consistent with the First Amendment will be a challenge. We are midstream in the rushing current of a new media landscape, but we shouldn’t lose confidence that our political system can unearth ways to tame this upheaval, just as it adjusted to the mass circulation of newspapers and the emergence of radio and television.

Ultimately, though, Americans will have to choose to do these things, which means we will have to repair the culture that underlies and shapes our politics. As Lincoln concluded in 1838, “Passion has helped us; but can do so no more. It will in future be our enemy.” What the country needed instead, he argued, was “general intelligence, sound morality, and in particular, a reverence for the Constitution and laws.” How to get there is the problem. But Americans have to expect a lot more than the status quo from our government and ourselves.