Vermont Sen. Bernie Sanders is trying to redefine progressive politics in a way that would in effect create a new wing of the Democratic Party. And Hillary Clinton is fighting Sanders over what it means to be a progressive, wary of being labeled a centrist or a moderate in an increasingly liberal party.
"I am a progressive who gets things done," she said in Thursday night's MSNBC debate in New Hampshire.
"The root of that word, progressive," she explained, "is progress."
Democratic activists, worried about the perceived centrism of Clinton, spent much of 2014 urging liberal hero Sen. Elizabeth Warren to run for president. So when Clinton started her White House campaign last April, her first moves were to take unabashedly liberal stands on gun control, immigration and racial policy in hopes of appeasing her party's left.
The surprising rise of Sanders has come in part because of the same problem that dogged Clinton in 2008: many liberal voters prefer another candidate.
But Barack Obama had a lot of other advantages against Clinton. He was a young and fresh face, a tremendous political speaker and a historic candidate who became the first black president.
The energy of the Sanders' candidacy is entirely about his left-leaning political pitch. And the Sanders' movement is one in direct contrast to the one the Clintons have built over the last three decades, a movement they consider to be avowedly progressive.
Back in 1990, Bill Clinton chaired the Democratic Leadership Council, an organization of centrist Democrats. The DLC created a policy arm called the Progressive Policy Institute.
The use of the term progressive was intentional. It was in contrast to "liberal," which conservatives had turned into an epithet describing people who supported so-called big government.
Clinton borrowed some of PPI's ideas and themes during his presidential campaign and later his administration. After the Clintons left the White House, Hillary Clinton was heavily involved in the creation of another Democratic think tank, the Center for American Progress.
PPI (which still exists but has diminished influence) is more centrist, while CAP, which is a powerful force in Democratic politics, is more liberal. But both organizations have looked to accomplish liberal goals with a focus on what is possible, " to "get things done," as Hillary Clinton says often.
This view of progressivism and the term progressive spread from the Clintons to other Democrats. In the period after the Iraq War, more and more Democrats were wary of been described as centrists, blaming the moderate wing of the party for being too eager to work with George W. Bush. Many Democrats dubbed themselves progressives in favor of being labeled under the banner of "liberalism."
Enter Sanders. He says his political views are those of a democratic socialist. But there is no defined socialist wing of the Democratic Party for Sanders to lead. And Clinton and other Democratic Party leaders have spent years defining themselves as progressives, a term they are unlikely to cede to Sanders' wing of the party.
"I've heard Senator Sanders' comments, and it's really caused me to wonder who's left in the progressive wing of the Democratic Party," Clinton said on Thursday night. "Under his definition, President Obama is not progressive because he took donations from Wall Street; Vice President Biden is not progressive because he supported Keystone; Senator Shaheen is not progressive because she supports the trade pact. Even the late, great Senator Paul Wellstone would not fit this definition because he voted for DOMA."
She added, slamming Sanders, "in your definition, as you being the self-proclaimed gatekeeper for progressivism, I don't know anyone else who fits that definition, but I know a lot of really hard fighting progressives in the Democratic party who have stood up time and time again against special interests, against the powerful on behalf of those who are left behind and left out."
Clinton argues correctly that both she and Sanders have advocated for tighter regulation on Wall Street. But Sanders has been much more strident in decrying what he calls the inherent corruption of the banking system as a whole.
"In my view, the business model of Wall Street is fraud," Sanders said during the debate, illustrating his dark view of the financial industry.
During the debate, Sanders laid out a series of proposals that described his view of progressive politics, most of which would make America more like Europe. But those views, as Clinton pointed out, contrast with Obama's style of governance.
"What we need to do is to stand up to the big money interests, and the campaign contributors. When we do that, we can, in fact, transform America," he added.
This article originally appeared on NBCNews.com.