In “Great Expectations,” Mr. Jaggers counsels Pip, “Take nothing on its looks; take everything on evidence. There’s no better rule.”

Like Pip, today we often take things on looks instead of evidence. This is especially true in politics.

Consider political dysfunction. Most Americans — including many scholars — base their understanding of what’s wrong with our politics today simply on how it appears. And who could blame them? Things look pretty clear.

According to social science data, polarization is the reason why politics is so dysfunctional. The data tell us that more polarized constituencies send more polarized members to Congress who, in turn, chose more polarized party leaders. These party leaders subsequently pursue a more polarized legislative agenda by exploiting congressional procedures for partisan gain. The practical effect? Congress is now more partisan and confrontational. And this leads to obstruction and gridlock, because the incentives for Democrats and Republicans to oppose each other in a polarized environment are greater than the incentives to bargain and compromise.

Social scientists tell us that we can expect this gridlock to continue as long as our electorate remains polarized. And so it seems that ending congressional dysfunction is inseparable from ending, or at least reducing, polarization. That is, if the ideological distance between the parties is what drives dysfunction, then our only hope is a public that somehow transcends current differences and elects candidates cut from a different mold — politicians more interested in solving America’s problems than are our current partisan warriors. Absent such changes in the electorate, reform-minded members seeking to make Congress work are left with no choice but to wall off the legislative process from the polarized conflict endemic in politics today and try their best to weather the storm.

Notwithstanding the apparent persuasiveness of such an argument, observers of American politics would do well to heed the advice Mr. Jaggers gives Dickens’ precocious protagonist: “Take everything on evidence,” he says. “There’s no better rule.”

On closer inspection, it turns out that the evidence on which the polarization thesis depends is hardly decisive. Rightly understood, polarization is more an optical illusion than a solid fact about American life. A better way to understand politics today is to focus on what members actually do in Washington.

Take Everything on Evidence
Most knowledgeable observers cite the same evidence to support the contention that today’s polarization is historically extreme and thus problematic.

To give just one representative example, take this Washington Post piece by Philip Bump, which describes the 114th Congress (January 2015–January 2017) as “the most polarized Congress in more than 100 years!” Bump cites Voteview, the repository of congressional roll-call votes that underlies the most widely used measure of legislator ideology, DW-NOMINATE. He reports that at no point in the past century has the political center, in between “liberal” and “conservative,” been so empty, and presents a slick interactive graphic to show just what the distribution of every Congress has been on this “liberal” to “conservative” spectrum. This is “a golden age of partisanship,” Bump tells us, adding that the 115th Congress may well end up even more polarized.

But such evidence doesn’t stand up under closer scrutiny.

The DW-NOMINATE algorithm uses just one kind of input to determine whether legislators are “liberal” or “conservative”: recorded roll-call votes. All recorded votes are weighted equally, and the algorithm assigns coordinates (generally in two-dimensional space) to each legislator such that if two members are closer together, they are more likely to vote in the same way on any particular vote. The resulting “first dimension” mapping for each legislator is generally interpreted as representing the legislator’s ideology on the “liberal-conservative” dimension.

By construction, this assumes that when two legislators vote in opposite ways most of the time, it is because one of them is “very liberal” and one is “very conservative.” But nothing in the algorithm actually supports using these labels instead of, say, “very likely to toe the Democratic line” and “very likely to toe the Republican line.” Many times, toeing the party line will mean acting out a certain ideological agenda — but many times, it won’t.

In fact, the conceptual difficulties go even deeper than this. The methodologies used in the algorithm are entirely reliant on what issues comprise recorded roll-call votes. If issues do not appear to divide each party, nothing in the data can tell us whether that is because the issues are not divisive or because the votes that would reveal them to be divisive simply do not appear, e.g., because they were successfully avoided. In other words, the ideology scores that DW-NOMINATE assigns are uniformly dependent on every vote that was recorded, but entirely oblivious to whatever members might think about issues that never receive roll-call votes.

Our political world is considerably more mixed up and uncertain than the standard story suggests. While political scientists can confidently state that Democratic and Republican legislators are voting more distinctly in the current political moment compared with recent decades, they have not really told us what this means.

An Alternative Explanation
It turns out that the conventional wisdom on polarization does not explain legislative behavior particularly well. That may be because polarization, properly understood, characterizes the appearance of politics, not its reality.

Today’s divergence between Democrats and Republicans in Congress does not indicate that members share no common beliefs or values. Instead, it reveals a political environment in which legislative leaders are extremely skilled at agenda-control and issue-suppression — at avoiding certain kinds of votes, for instance.

Republican leaders, in particular, have refined the art of restricting roll-call votes to just those matters that serve to unify their caucus. Debates that produce votes on amendments that have not been carefully weeded out by the leaders have become vanishingly rare. There are no more open rules in the House, for example. And Senate leaders utilize a complex assortment of rules and practices to exert greater control over the legislative process than at any previous point in the institution’s history. The principal means by which leaders establish such control is their ability to block amendments on the Senate floor, which they use to structure the amendment process so as to permit only uncontroversial amendments. This protects senators from having to cast tough votes that could be used against them in their effort to secure re-election.

Given this dynamic, measured polarization, of the sort used by DW-NOMINATE, is largely an indicator of the majority party’s active dominance of the agenda-setting process within Congress. Of course, setting the agenda gets harder when members of the majority party do not agree on policy. So when more and more issues divide a given party’s members, more and more issues must be kept off the agenda in order to prevent the party coalition from fracturing. Fear of such a fracturing in today’s environment is what prompts party members who can’t agree on policy to empower their leaders to keep divisive issues off the agenda.

This helps explain the near-exclusive control of the legislative process by party leaders today. Leaders use their control to keep the focus on issues that unite their partisan colleagues, while drawing favorable contrasts with the other party. The result is to create the appearance of polarization between two parties, despite the fact that the members within a single party disagree on quite a lot. In this way, declining cohesiveness of a party’s membership ends up creating the impression of “stronger,” more ideologically homogenous parties — “polarization.”

What empirical measures like DW-NOMINATE are really picking up on is the stage-managed process of agenda-setting, not polarization. This is easy to overlook because the result — gridlock — is the same regardless of the underlying cause.

For example, both parties are divided internally on such pressing issues as health care, immigration, government spending, and gun control. This prompts leaders to avoid taking up legislation dealing with these issues and to structure the legislative process to prevent other members of Congress from doing so. “Gridlock” ensues.

More specifically, leaders work hard to keep divisive issues off the agenda for as long as possible. When that is no longer an option, they resort to crafting must-pass legislation behind closed doors with little or no input from the rank-and-file. Leaders then wait until the last minute to unveil the legislation in order to confront members with a fait accompli, thus increasing the chances that the bill will pass while minimizing the exposure of partisan divisions.

Leader control of the House and Senate is thus crucial to perpetuating the mirage of partisan unity in the Democratic and Republican caucuses. And this, not party polarization, is what drives political dysfunction.

Solving the Real Problem
Accurately diagnosing the ailments from which the body politic currently suffers is the first step in curing it. But the polarization thesis impedes a proper diagnosis.

Reforms designed to increase Congress’ lawmaking capacity by walling off the legislative process from polarized conflict will only make the situation worse. This is because minimizing conflict makes it easier for party leaders to control the legislative process. The end result is to perpetuate the stage-managed process that is, in reality, responsible for today’s dysfunction — as well as the widespread perception of polarization.

To say that polarization is not the cause of our political dysfunction is not to say that Americans agree on everything. Far from it. There are significant differences both within and between the two parties. What is not supported by evidence is the idea that Democrats and Republicans in Congress have well-defined and mutually exclusive visions for federal policy — a precondition for polarization. This idea is made plausible only by a relentless focus in politics and media on a few issues that divide the two parties. But the reality is much messier than that.

The good news is that curing Congress’s dysfunction and ending gridlock does not require a Herculean effort to rewire the political DNA of millions of Americans and thereby eliminate polarization from our politics. We don’t need different voters, or even an entirely new crop of representatives. Instead, what we need is a more freewheeling process in the House and Senate that gives our legislators the chance to grapple with the key issues of the day without knowing exactly what kinds of compromises they will be able to end up at.

Such an aired-out process would allow progress on issues that seem intractable in the current stifled, stage-managed process that prioritizes the preservation of the partisan status quo above all else. We would find out in a hurry that our representatives are, like the rest of us, not sure what the appropriate actions are in many policy areas. Watching members grope toward acceptable solutions in real time would reinvigorate the connection between the legislature and the public, creating a sense of real stakes and real accountability. This would be a salutary alternative to the current sense that when we vote for someone to go to Capitol Hill, all we are really doing is picking which party’s leadership to put in charge.

If this sounds like wishful thinking, that is only because we have been conditioned to see political conflict as negative, something to be avoided. Yet managing conflict in a pluralistic society is one of Congress’s key functions. Only through such a process can policy outcomes be legitimized and the losers of a legislative debate mollified. And despite its messy appearance, a deliberative process remains the most efficient way to identify durable compromises on controversial issues.

There will certainly be times when such compromises aren’t possible. But even in those scenarios, the outcome — inaction — contributes to the conflict’s resolution. By raising the public’s awareness of an issue, a contentious debate in Congress elevates the issue and ensures that it will be on voters’ minds when they head to the polls. In that way, elections help dislodge debates that have stalled by replacing members on one side or the other.

A more freewheeling and aired-out process in Congress may be disruptive to the efforts of party leaders to maintain the appearance of partisan unity in the face of internal division, but it would empower the public with more information. And it would lead to more stability in the long term by aligning the efforts of Democrats and Republicans in Congress with the expectations of the American people.

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