Andrew Kohut is founding director and former president of the Pew Research Center. He served as president of the Gallup Organization from 1979 to 1989.

The recent polarization of American politics has been far more obvious on the right than the left. The emergence of the tea party movement and its influence in Congress has brought to the fore political values that are more conservative than those of the average voter.

But polarization is not a one-way street. While Republicans have become more conservative, Democrats have grown more liberal. The Pew Research Center’s values surveys, spanning 1987 to 2012, show that Democrats as a whole have moved to the left in recent years. They are much more socially liberal than they were even a decade ago, more supportive of an activist government, more in favor of increased regulation of business.

Under the more centrist Obama administration, the leftward movement of Democratic voters has been of limited political consequence. Most of the change on social policies such as same-sex marriage and marijuana legalization has come at the state and local levels. However, looking ahead to 2016, the viability of liberal Democrats has emerged as a critical question for the Democratic Party. Even as conventional wisdom coalesces around Hillary Rodham Clinton as the establishment candidate, the success of prominent progressives — Sen. Elizabeth Warren of Massachusetts and New York Mayor Bill de Blasio come to mind — means the party could face an ideological divide in 2016.

And the progressives, or liberals, seem to have the momentum. Gallup recently reported that liberal self-identification has edged up to its highest level in more than 20 years. Similarly, Pew Research’s values surveys have documented increasingly liberal beliefs among Democrats on social, economic and regulatory matters. While the move leftward has occurred among moderate and conservative Democrats as well as liberal ones, liberals have either moved further left or hold more intense views than moderates and conservatives.

And that’s where comparisons with polarization on the right begin to break down. Although liberal Democrats have swelled in number, the advantage within the party still rests with moderates and conservatives. In Pew’s nationwide survey in January, only 34 percent of Democrats called themselves liberal, compared with 63 percent identifying as moderate or conservative. In contrast, conservatives are a clear majority (67 percent) in the GOP, while self-described moderate and liberal Republicans make up just 32 percent of the party.

This might ensure that, despite the leftward trend, Democrats will not become identified as an extremist party like the GOP. By 54 percent to 35 percent, a January Pew Research poll found that the public continues to see the GOP rather than the Democrats as the party that takes more extreme positions.

Yet the gap within the Democratic Party is real — and it is not just ideological but demographic as well. Women and white voters make up a disproportionate share of liberals; liberal Democrats are also more affluent and better educated than the party as a whole. In contrast, moderate and conservative Democrats are more often male, poorer, less educated, and African American or Latino.

While Democrats share many core values, there are a number of ways that liberals differ sharply from the rest of the party and the rest of the country.

First, in-depth Pew Research surveys find that many liberals are cynical about achievement. Most don’t agree with the statement that “people can get ahead if they work hard,” and relatively few fully agree that they admire people who have become rich through hard work.

Second, liberals give low priority to dealing with the budget deficit, a major concern for much of the electorate, and they are the only political segment that expresses majority support for paying higher prices for the sake of the environment.

Third, liberals are also significantly to the left of the rest of the Democratic Party on social issues. Unlike other Democrats, few liberals say prayer is an important part of their lives, most strongly favor same-sex marriage, nearly all support abortion rights, and a majority support a path to citizenship for illegal immigrants.

1 of 18 Full Screen Autoplay Close Skip Ad × Myths of 2014 View Photos Fact or fiction? A collection from Outlook’s popular Five Myths series. Caption Fact or fiction? A collection from Outlook’s popular Five Myths series. MYTH: Sanctions never work. “The most complete academic studies on the matter show that sanctions lead to concessions from the targeted government in one out of every three or four cases,” writes Daniel W. Drezner in “ Five myths about sanctions . “That is a far cry from never working.” Here, President Obama and German Chancellor Angela Merkel leave a joint news conference at the White House in May. The leaders discussed additional sanctions to punish Russia for its incursion into Ukraine. Charles Dharapak/AP Buy Photo Wait 1 second to continue.

And fourth, on foreign policy, most liberals reject the idea that the best way to ensure peace is through military strength; unlike other Democrats, a majority would find it acceptable if another country became as militarily powerful as the United States.

On the politically charged issue of the day, economic inequality, majorities of both liberal and more moderate Democrats agree that the government should make a significant effort to shrink the gap between rich and poor and reduce poverty. However, even there, most liberals think that government action can make a big difference, while moderate and conservative Democrats don’t share their optimism.

Liberal Democrats are more approving of and more loyal to President Obama on a range of issues and policies — particularly health-care reform and his handling of the budget deficit — than more moderate Democrats. Liberals also rate Clinton higher than moderate Democrats do, though they were largely not on her side during her 2008 presidential bid, once Obama entered the picture. In that regard, it is instructive to note how quickly liberals have flocked to Elizabeth Warren: Fifty-four percent of liberal Democrats hold a favorable opinion of the senator from Massachusetts, compared with just 35 percent of moderate and conservative Democrats, many of whom don’t know much about the high-profile progressive.

How much sway will liberal Democrats hold in the party, especially as the 2016 election approaches? Although they are a minority of Democrats nationwide, liberals are more politicized and make up a disproportionate share of primary electorates. For example, in 2008 they made up 56 percent of New Hampshire Democratic primary voters and 54 percent of Iowa caucus-goers.

In the shutdown era, Democrats have had a more moderate image nationwide than the tea-party-burdened GOP. But that image may be at risk if liberal Democrats set the pace for the party. We could see them rally around a progressive leader — Warren, de Blasio or some yet-to-emerge candidate — who speaks their language of economic populism. If the agenda of this new New Left drives Democrats’ choices, it might weaken the ideological and demographic coalition that has led the party to victory in four of the past six national elections.

Read more from Outlook:

Andrew Kohut: The numbers prove it: The GOP is estranged from America

Friend us on Facebook and follow us on Twitter.