Democratic U.S. presidential candidate Hillary Clinton (L) listens to Senator Bernie Sanders speak during a Democratic debate hosted by CNN and New York One at the Brooklyn Navy Yard in New York April 14, 2016. REUTERS/Lucas Jackson

In its final stages, the Clinton-Sanders contest has been distressingly dominated by arguments over party rules while Donald Trump consolidates his control over the Republican Party and begins his general election campaign. But for most of the primary season, the two chief contenders have waged a civil campaign rich in discussions about the best path to a progressive future and the policies to get there. The primary phase will be over soon and Senator Sanders and Secretary Clinton will work hard to unify the Democratic Party with a platform that reflects the voices and priorities of both victor and runner-up.

The conventional wisdom about extended primary election campaigns is that the front-runner is influenced on issues like the economy or climate change, and pulled to the left (or right, as the case may be) by a challenger with a strong agenda. And indeed, injecting issues into the election is a key way to advance debates and sharpen policies.

This year, in the Democratic primaries, which quickly became a two-person race, many have seen Senator Bernie Sanders in that role. But it takes nothing away from Senator Sanders, and the millions of voters he has mobilized, to observe that deeper currents are at work that have created a political climate which has sharply influenced both him and Secretary Clinton.

The sleeper story of this year's Democratic primaries is the role of social movements.

Why do both candidates now support an end to deportations, a higher minimum wage, justice for Flint, and other progressive stances? Because social movements moved them.

Occupy Wall Street captured the nation's attention and made income inequality central in the national debate. While some have criticized Occupy and subsequent social movements for not pivoting to an electoral strategy, as the Tea Party has done, it is undeniable that it shifted the national discourse, influencing President Obama's final years in office, buttressing political leaders like Elizabeth Warren and Bill de Blasio, shaping the positions of Hillary Clinton well before a strong primary challenger emerged, and creating a more favorable climate for a candidate like Bernie Sanders.

United We Dream moved the Obama administration, despite its earlier protestations about the scope of its executive authority, to take historic steps toward relief of the threat of deportation for young undocumented people and their families, prompting the two Democratic candidates to go even further, opposing the continuing raids being carried out by the administration.

Black Lives Matter has reopened the debate over the 1994 crime bill and its consequences, leading both Hillary and Bill Clinton to reassess the policies they pursued, and confronted Bernie Sanders as well, shifting his rhetoric, his policies and even his staffing.

On climate change, communities of color, indigenous communities, ranchers, and many others on the frontlines of fossil fuel extraction and infrastructure projects, are winning victories and mobilizing en masse to support the Clean Power Plan. President Obama stopped new coal leases on public lands and Senator Sanders is riding the movement's momentum to stake out even bolder positions on issues like fracking.

And the Fight for 15, led by courageous workers in fast food and other industries across the country, has attracted both candidates to its cause and had a visible impact on Secretary Clinton's sense of what is possible and what she has pledged to fight for.

The impact of social movements is not limited to the Presidential contest, or to the Democratic side. Why is the Republican governor of North Carolina faltering, and why is everyone from the NBA to Fortune 500 companies boycotting the state over issues critical to the trans community, which couldn't even get respect from the larger LGBT movement only a few years ago? Because of the strength and insistence of a social movement. Because people shook things up. And why are we beginning to see proactive voting rights victories like automated voter registration and the restoration of rights to formerly incarcerated persons? Because of social movements like North Carolina's Moral Mondays protests, which are helping shift the national debate away from spurious allegations of voter fraud to meaningful conversations about barriers, access, and participation.

Pressure from social movements is not always welcomed by candidates or officeholders, and is often designed to make them uncomfortable. But it is essential to building a strong progressive future, and the best thing that can happen after January 20, assuming we elect a progressive President - and if we don't, a staunch course of resistance will be necessary - is for the vibrant social movements we have seen on income inequality, criminal justice and immigrant rights to remain in force, supporting the new President when on the right track and insisting on accountability when on the wrong track.

Candidates and Presidents are important, and it is vital to elect the right ones. But what they can do - and sometimes, what they must do - is shaped by the force of social movements. That was true of Lincoln and abolition, of FDR and the New Deal, of LBJ and the civil rights movement, and of Obama and health care and financial reform, and it will be true of whoever takes the oath of office in 2017 and for the critical years to follow.

First published at DemocracyAlliance.org.