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How the left is reshaping Clinton's campaign

Clinton's moves on Black Lives Matter and college debt are just the latest examples of how progressives are putting pressure on the Democratic front-runner.

Democratic presidential front-runner Hillary Clinton met privately with Black Lives Matter activists after an event Tuesday in Keene, New Hampshire. It was the latest sign the movement has injected itself into the 2016 presidential race.

The movement, which formed in the wake of last year’s racially charged protests in Ferguson, Missouri, has already disrupted speeches by two other 2016 Democratic hopefuls -- Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O’Malley -- and it was only a matter of time before they targeted Clinton.

RELATED: Inside Hillary Clinton's aggressive new campaign plan

While the Black Lives Matter movement’s confrontational tactics have been controversial, their impact is unquestionable. Pressure from the movement has led all three leading Democratic candidates to put out comprehensive criminal justice reform plans. The candidates have woven racial justice into their stump speeches, uttered the words “black lives matter” in public events and said the names of African-Americans killed by police.

It’s just one example of progressive grassroots activists shaping the 2016 Democratic primary, with candidates often responding to priorities set by the movements. At a time when general election success will be determined largely by the ability of candidates to turn out Democratic base voters, activists can convince candidates it’s in their best interest to support liberal causes. And that's especially true for Clinton, who wants to show she can unite the Democratic Party behind her.

On Monday, Clinton rolled out a $350 billion college affordability plan that included a proposal for debt-free public college.

"If you had any doubt that the populist, progressive Warren wing is the driving force in the Democratic Party today, the emerging competition among Democratic presidential candidates to establish the biggest, most comprehensive plan to tackle student debt should erase it."'

The former secretary of state has long talked about college affordability. During her 2008 presidential campaign, she would ask audience members to shout out their student loan rates. But advocates believe her recent plan is much bigger, came sooner in the campaign cycle and was made a higher priority than it otherwise would have been without their pressure.

Clinton now promises to make college affordability a centerpiece of her campaign, along with criminal justice reform, which she discussed in the first policy speech of her campaign.

Debt-free college is a new idea that rocketed to the top of the progressive agenda at lightning speed. The term was on few peoples’ radars until the liberal think tank Demos published a widely shared white paper on the idea in September.

The Congressional Progressive Caucus endorsed the idea in the spring, followed by some liberal senators. “I'm hopeful that debt-free college is the next big idea," New York Sen. Chuck Schumer said in April.

Now, all three leading Democratic candidates have adopted the idea. “For months, [Progressive Change Campaign Committee] members and think tank Demos engaged presidential campaigns on this issue. Together with allies, our organizing in Congress and early presidential states put this idea on the map -- and shifted the 2016 debate,” said Adam Green of the PCCC, which led debt-free college advocacy efforts.

Last year, facing the prospect of a largely uncontested Democratic primary, many progressive groups realized they had to do something. Their goal was to push for the most progressive nominee possible, whether it meant pressuring Clinton to move to the left or supporting an alternative like Massachusetts Sen. Elizabeth Warren, whom some groups tried to draft into the 2016 race.

The battlefield is between Clinton's ears, some activists quipped.

While the groups used different tactics, and are often not in in cooperation with each other, the effect on the 2016 field is notable. The result is a presidential primary field that is decidedly more progressive on a person-for-person basis than the one Democrats were presented with the last time they had to choose, in 2008.

"If you had any doubt that the populist, progressive Warren wing is the driving force in the Democratic Party today, the emerging competition among Democratic presidential candidates to establish the biggest, most comprehensive plan to tackle student debt should erase it,” said Charles Chamberlain, executive director of Democracy for America.

And confrontational tactics are appealing to Black Lives Matters activists after they watched other groups get aggressive and earn tangible policy accomplishments.

A year ago, it was DREAMers who were interrupting campaign events and demanding to have their issues put at the top of the candidates’ agenda. Young undocumented immigrants confronted Clinton in September during her first trip back to Iowa since her 2008 defeat. And they interrupted an event in Maryland where both Clinton and Martin O’Malley spoke.

Now, interruptions from DREAMers have disappeared from Clinton and O’Malley events since both candidates have, to a large extent, met the demands of activists. Now, instead of interrupting Clinton, some DREAMers work for her campaign.

Earlier, it was LGBT rights activists who heckled President Obama and interrupted senators at the liberal Netroots Nation conference, the same gathering at which Black Lives Matters activists disrupted Sanders and O’Malley last month.

Partially in response, the Obama administration moved to end the "don’t ask, don’t tell" military ban on openly gay service members and then stopped supporting the Defense of marriage Act. In June, the Supreme Court made gay marriage legal in all 50 states.

And the targeting of Sanders by Black Lives Matters activists shows that even the most progressive candidates are not immune to pressure from the grassroots.

Still, the pressure tactics have major limits. Despite a long and active movement against the Keystone XL pipeline, Clinton has yet to take a position on the controversial project and the White House has yet to veto it. Climate activists interrupted a Clinton town hall in New Hampshire last month, but failed to get Clinton to oppose fossil fuel production on federal lands.

And the same is true for trade policy, where no amount of labor union pressure has been able to compel Clinton to come out against the Trans-Pacific Partnership so far.

Clinton and her fellow candidates ultimately control their message, but they respond to incentives and pressure.