With a right-wing populist in the White House and his ideological brethren thriving across a broad swath of Central and Eastern Europe, it's perfectly understandable that pundits and academic analysts have devoted considerable time and attention to reflecting on threats to liberal democracy from the right. Those threats are real and important. But that doesn't mean that the dangers confronting our political system come entirely from one ideological direction.

Trumpism (for want of a better term) is just one expression of the underlying source of our problems, which is the trend toward increasing political polarization. Conservative parties are moving rightward, but progressive parties are also moving left — and both are directing their fire at least as much toward the centrist establishments of their own parties as they are toward their most distant ideological opponents.

This presents an ominous possibility — namely that we may have entered an era in which polarization drives an emboldened left and right to flee the center and then provoke one another into a series of reactions and counter-reactions that make polarization ever-worse, ultimately producing a breakdown of liberal democratic government altogether. What form of government arises from that collapse is anyone's guess, but it isn't likely to be an improvement on the status quo.

For a glimpse of how such a series of events could unfold, consider a recent essay by Jedediah Purdy in Dissent and the response it inspired on the part of one prominent liberal pundit who writes from a perch at a leading think tank of the center left.

Purdy's review essay takes on several new books about the Trump administration's assault on liberal norms. His treatment of them is highly tendentious. Yet the polemic is nonetheless worthwhile. The centrist consensus of the past generation does need to be shaken up, with a new consensus being formed to take its place, and for that reason it's helpful for readers to have a bold and ambitious leftist agenda laid out for debate and discussion. In Purdy's view, that agenda needs to have several elements:

For one, we need substantial redistribution, starting with marginal tax rates at the 70 percent levels that lasted until the Reagan-era cuts of the 1980s. For another, we need entirely new institutions of planning and social provision, such as universal family leave and child care to help make the economy more humane, family life less exhausting, and get closer to gender equity. We might also have to do much more to strengthen labor unions, to the point of considering radical measures such as mandatory unionization, which is often the only way to break management's hold on labor in large firms. It could also mean a new dispensation of basic legal rights, such as granting residents, rather than only citizens, the right to vote. [Dissent]

Given how many aspirants to the Democratic presidential nomination in 2020 have already embraced elements of Bernie Sanders' democratic-socialist agenda from 2016, there's a decent chance that a number of these proposals could end up championed by the man or woman who wins the presidency less than three years from now. What would be the likely result?

Ian Millhiser of the liberal Center for American Progress played out one scenario in a lengthy Twitter thread that began with a full-throated endorsement of Purdy's essay and policy proposals.

If the left and center-left "want to regain the upper hand," Millhiser claims, they desperately need "to deliver big, transformative change to people who are knocked back on their heels right now." The problem, though, is that the American political system is filled with "veto points" — "the filibuster, congressional committee structure, a Supreme Court dominated by Republicans whose majority is increasingly willing to embrace made-up legal theories in order to strike progressive laws" — that enable the right to thwart such ambitions. The result is that Democrats go tepid for fear of overpromising, which makes them look like "sellouts and wimps."

But what if the party overcomes these obstacles to enact a genuinely ambitious leftist agenda? In that case, Millhiser writes, Democrats would still face the possibility that the agenda would get struck down by a 5-4 majority of the Supreme Court (led by Justice Neil Gorsuch, whom Millhiser makes a point of describing as an "illegitimate member of the court"). And that's where things would threaten to get even uglier, with Democrats coming around to the view that they need to expand the number of justices on the court in order to pack it with liberal jurists who would overturn the right's move against the left.

In the original thread, as well as in subsequent responses to critics, Millhiser showed that he recognizes that attempting to replicate FDR's own failed effort overcome conservative opposition to the New Deal by packing the court with liberals could prove perilous both for the Democrats and the American political system as whole by more egregiously violating the very norms that Republicans have been testing in recent years. Yet Millhiser insists that the extremism of the GOP may well make such moves necessary for the left. He's not happy about it, but he does sound resigned to it.

And therein lies the problem — and the danger.

Of course those on each side of a serious civic disagreement consider their own transgression of settled norms to be fully justified by the prior violation committed by the other side. That's the logic of escalation. It plays out between nations in the run-up to a war, just as it can unfold within a single country that's hurtling toward institutional paralysis, civil unrest, and an extra-constitutional power grab in the name of preserving law and order.

In the scenario Millhiser lays out, the left is fully justified in doing anything and everything necessary to enact a strongly progressive agenda because opposition to it is simply illegitimate. If we assume a political system based on simple majoritarianism at every level, and then also assume that a bare majority of the American people in 2018 would support a more leftist approach to policymaking than we've seen since at least the 1960s, then there might be considerable truth to this.

Yet note that even in this hypothetical case, tens of millions of Americans would presumably still oppose such an agenda. And not just oppose it — strongly oppose it. In fact, it has been the incredible intensity of opposition on the part of tens of millions of Republicans to Democratic policy ambitions over the past few decades that has empowered them to use the many veto points within American government to scuttle the efforts of progressives to enact "big, transformative change."

If significantly fewer Americans opposed the progressive vision for the future of the country, these efforts would have failed and the left would have prevailed years ago. Likewise, if the democratic-socialist message resonates in 2020 with something like a supermajority of citizens, the left will be able to overcome America's many counter-majoritarian checks to enact its preferred policies, just as FDR was ultimately able to do after his own bid to pack the Supreme Court ended in defeat and humiliation.

On the other hand, if many more Americas aren't persuaded to embrace the progressive vision of the country's future — if opposition remains widespread and intense across much of the nation — then the left is going to find its ambitions frustrated. But it won't necessarily be because the right is doing anything illegitimate. It will be because tens of millions of Americans strongly disagree with the left.

It will be, in other words, because America remains sharply and deeply divided.

In such circumstances, our system of government is designed to allow the opposition to throw a wrench into the gears of government. The proper response to that situation isn't to find a way to override the blockage. It's to find a path forward that commands greater consensus. If that can't be done, the result may be paralysis. That's bad. But not as bad as one side in a deeply divided nation ramming through its policy preferences over the strong opposition of nearly half the country, which would be an outcome guaranteed to produce a civic disaster.

Tens of millions of angry voters can make an awful lot of mess. Wishing them away or acting as if they don't get a say in our public life simply isn't a serious response.