Since the Democratic Party's liberal base is smaller than the Republican Party's conservative base, this is more important for Democrats than for Republicans. Since 1976, no Democrat has been elected president without winning at least 60 percent of the moderate vote cast for the major parties.
Moderates, the largest component of the electorate and the Democratic coalition, are not liberals in disguise. Nor are they a mushy middle. They are a distinct group: center-left on social issues, middle of the road on economics, center-right on foreign policy and more skeptical about the role of government than liberals are.
If moderates are such a crucial and coherent political force, why is U.S. politics so polarized? The answer lies in three structural features of the political system that reduce moderates' influence: the primary system, the congressional redistricting system and the congressional leadership system.
The primary electorate is a small, unrepresentative portion of the overall electorate. In the highly visible 2010 election season, for example, only 7.5 percent of all voting-age Americans took part in congressional primaries — actually higher than in past years.
This primary electorate is dominated by the parties' base voters — which is not true in general elections. That's why so many Americans say they are unhappy with their choices in November. Regardless of their attitude toward bipartisan governance, politicians are under intense pressure to cater to their primary voters. All the more so after the upheaval of 2010, in which primary voters rejected longtime incumbents.
Congressional districts are drawn in ways that make nearly all of them safe for one or another of the major political parties. Considered in tandem with low-turnout primaries, gerrymandering further diminishes the influence of moderates.
The average percentage of House incumbents winning with supermajorities has steadily increased during the past five decades. Even the hotly contested 2010 congressional elections resulted in a net Republican pickup of just 14 percent of the entire Congress. While most scholars and reformers focus on either primaries or redistricting, it is the combination that systematically reduces the impact of moderates.
So, finally, does the current system of selecting the House speaker and the Senate majority leader. The dominance of each party's caucus in these elections means the leaders reflect a majority of the majority — nearly always a minority of the entire body. The selection process does not promote compromise but reinforces the influence of each party's base.
While there is no easy fix to any of these problems, structural and procedural reforms can make a difference.
First, states should adopt more-open primary systems — ranging from simply allowing nonaffiliated voters to participate, to instituting completely open primaries, such as the Top Two Primaries Act adopted in California last year.
Second, states should take redistricting out of the hands of legislatures and entrust it to nonpartisan commissions — as some states, such as Iowa, already have.
Third, the congressional leadership should be elected by a supermajority of, say, 60 percent. Unless one party enjoys an overwhelming edge, the first vote in each new Congress would test the majority party’s ability to create the bipartisan coalitions that are integral to effective government.
As our problems mount, too many Americans are losing confidence in the future. Restoring that confidence requires systemic reforms that begin to move us from the politics of point-scoring to a new politics of problem-solving.
William Galston is the Ezra Zilkha chair and senior fellow in governance studies at the Brookings Institution. Elaine Kamarck, a public policy lecturer at Harvard University’s Kennedy School of Government, is author of “Primary Politics: How Presidential Candidates Have Shaped the Modern Nominating System.”