Jeff Stonecash studies the changing electoral bases of American political parties. He is emeritus Maxwell Professor at Syracuse University.

The political parties in Congress are deeply polarized. Voters are also. Evaluation of presidential job performance is increasingly driven by party identification. The percentage of voters choosing to identify with a party is increasing, and those who identify with a party are consistently voting for the candidates of their party. What is driving this division and how did we arrive at this situation? While some commentators single out gerrymandering, Tea Party “birthers,” and machinations by figures like the Koch brothers, these explanations miss the point. The sources of polarization are substantive, long-developing, and unlikely to disappear soon.

Two factors have produced our polarized politics. First, changing social conditions and government actions have combined to prompt fundamental disagreements about what and how much government should do. Second, a long-term realignment brought this debate into sharp focus. In short, today’s polarization is the product of today’s issues and yesterday’s political realignment.

The paramount debate in American politics is how much government should help individuals and who will pay for this. This debate has grown in intensity alongside several trends. Ideas changed about how much individuals can be held responsible for their situation. More studies concluded that many people are overwhelmed by circumstances they cannot control. Inequality has steadily increased. Social programs have become increasingly costly. More of the tax burden has shifted to the affluent.

The reactions of liberals and conservatives to these developments have been vastly different and those divergent reactions are driving the debate. Liberals have become steadily more supportive of programs to help people. They support expansion of an array of social programs that provide benefits– disability benefits, Medicaid and Obamacare, grants to attend college – and higher taxes on the most affluent. Their presumption is that people have needs, opportunity has been unfairly distributed, and government is the vehicle to respond.

Conservatives have reacted by gradually becoming more adamant that government is doing too much. They still see individualism as central to how America should operate. They argue that a concern for expanding opportunity has morphed into untouchable entitlements. They see the emergence of welfare and other social programs as destructive of what made America successful. Their central concern is that government is coming to support too many people, creating dependency rather than hard-working individuals. In this view, the reason many people are failing is because they are losing the inclination to adopt the behaviors that help people achieve.

Furthermore, these programs are increasingly paid for by those who achieve. The percentage of federal income tax revenues from the top 10 percent has steadily increased, creating a more progressive income tax system. They also argue that when the distribution of the benefits of social programs is included, the overall impact of the tax system is now significantly redistributive. The position of stopping tax increases has become entrenched, and no Republican in Congress has voted for a tax increase since 1993.

The result is a fundamental difference between liberals and conservatives regarding how much government should help people. It is the basis for an increase in ideological conflict and creates intense battles over the legitimacy and funding of social programs. The battle has involved changes in welfare programs, limits on the ability to declare personal bankruptcy, tax cuts and Obamacare. It is not a debate that is likely to go away because none of the precipitating conditions are likely to change in the near future.

Washington is different from 30, 40 and 50 years ago because the substance of the debate and the social and policy conditions are different. Government does more. Tax burdens are distributed differently. There are those who suggest that policy differences are largely the same and the only difference over time is that voters have sorted themselves out more between the two parties. To make that argument is to dismiss the policy developments of the last 50 years and to assume the context of the 1950s and 1960s still prevails. The debate is more intense because the stakes have changed.

How did we get here? As recently as the late 1990s, a central theme was that elections were candidate-centered, and few would have expected the level of party discipline in Congress that we see now. In reality, the separation of congressional results from presidential results was temporary. A long-term realignment was occurring.

Beginning in the 1960s, Republicans began to pursue a more conservative electoral base, particularly in the South. Democrats, based for a century in the South, pursued a more liberal base, which was primarily in the north and in urban areas. Presidential results changed faster than congressional results, creating the appearance of candidate-centered elections for Congress. Eventually the South moved Republican and the Northeast moved Democratic. This long-term realignment produced the pattern shown in the figure below. It displays the correlation between presidential and House results and the presence of split outcomes from 1900-2012. Beginning in the 1970s, the correlation between presidential and House voting increased sharply, and the number of districts who split their vote for president and House declined. By 2012, only 7 percent of districts had split outcomes.

For a long time, Republican House candidates in particular could not capitalize on presidential results in districts. As late as 1990 Republicans won only 51 percent of the House districts George H.W. Bush won in 1988. In 1994 the party made major gains and in 1996 it won 89 percent of the seats won by its presidential candidate. In 2012 Republicans won 96 percent of these seats. After decades when many Republican House members had to worry that their electoral base was not sympathetic to conservative positions, they now can count on a base that is truly supportive.

Polarization thus derives from the combination of a growing debate about the role of government and a realignment that has brought Republicans a more secure base. Each party may have a few extremists, but in large part they are representing their constituents. The current polarization is not because Republicans have gone off the deep end, but because of fundamental policy disagreements, prompted by the central questions facing American society.

So long as those issues remain unresolved, the polarization that they foster is likely to be with us as well.

Further Reading

This is the latest post in our ongoing series on political polarization. The previous posts are listed below.

What we do know and don’t know about our polarized politics.

American politics is more competitive than ever. That’s making partisanship worse.

Polarization we can live with. Partisan warfare is the problem.

How political polarization creates stalemate and undermines lawmaking.

Electing more women to Congress isn’t a solution for polarization.

How U.S. state legislatures are polarized and getting more polarized (in 2 graphs).

How ideological activists constructed our polarized politics.

Our politics may be polarized. But that’s nothing new.

Our politics is polarized on more issues than ever before.

How race and religion have polarized American voters.

Can young voters break the cycle of polarization?

Americans aren’t polarized, just better sorted.

How politically moderate are Americans? Less than it seems.

The real extremists are American voters, not politicians.

How better educated whites are driving political polarization.