Why the 'Run Warren Run' movement is calling it quits. (Hint: Bernie Sanders plays a part)

A pair of politically active groups are giving up their quest to have Massachusetts Senator Elizabeth Warren enter the 2016 presidential fray.

Massachusetts Senator and liberal icon Elizabeth Warren has has long said she isn't running for president. Now, after months of ignoring her protestations, Sen. Warren's strongest backers are finally taking no for an answer.

"Today we announce the suspension of our campaign to draft Elizabeth Warren into the presidential race," MoveOn.org and Democracy for America, the two groups behind the "Run Warren Run," movement, announced in an opinion piece in Politico.

The movement was founded in December 2014 expressly to persuade Senator Warren, a liberal hero, to run for president. Its investments were not insignificant: The six-month-long campaign collected 365,000 signatures, spent $1.25 million, opened three field offices, hired more than a dozen organizers and scores of volunteers, and earned dozens of endorsements.

So why is it closing shop?

For starters, it finally listened to Warren.

"No. I am not running and I am not going to run," Warren said in a March 2015 interview on the “Today” show, ruling out the possibility in both the present and future tenses.

"We would still love for her to run," Ben Wikler, Washington director of MoveOn, told CNN. "But she has been clear and consistent and at this point it doesn't feel like there is an obvious way that we could change her mind."

What's more, others have appeared to adopt Warren's message – or at least her language.

To illustrate, let's play a game of 'Who said it?'

"The deck is still stacked in favor of those at the top.”

Who said it? Hillary Clinton, half of the famously centrist Democratic power couple who has moved to the left in her latest presidential campaign.

Let's try another: "There's something wrong when CEOs make 300 times more than the typical worker."

You got it – Clinton again, whose very campaign theme is to be the champion of "everyday Americans."

"Just listen to Hillary Rodham Clinton speak in these early days of her campaign, and the populist, Warren-esque language on income inequality and social mobility is unmistakable," Linda Feldman reported for the Monitor in an April piece titled, "Elizabeth Warren may not be running, but she's in the 2016 race anyway."

Clinton's not the only one. Former Maryland Democratic Gov. Martin O’Malley launched his campaign with a populist attack on big banks and corporate giants.

“We cannot rebuild the American dream here at home by catering to the voices of the privileged and the powerful,” he told supporters in Baltimore, echoing Warren's message.

Mr. O'Malley has a strong progressive record: as governor of Maryland, he tightened gun control, legalized same-sex marriage, abolished the death penalty, and worked toward legalizing marijuana, liberal achievements he is flaunting in an effort to claim the progressive mantle. Since Freddie Gray's death and the ensuing protests in Baltimore, however, he has been hampered by his past as a get-tough-on-crime mayor of Baltimore whose "broken windows" policies, critics say, unfairly targeted minority neighborhoods.

But perhaps the most convincing Warren surrogate is Sen. Bernie Sanders (I) of Vermont, a self-described Democratic socialist and diehard liberal who best captures Warren's progressive base. Senator Sanders recently surged in early-state polling and appears best positioned to become the progressive standard-bearer as he seeks the Democratic nomination.

“To the billionaire class, I say your greed has got to end,” Sanders said in his announcement speech in Vermont.

As MoveOn and Democracy for America wrote, "Although Run Warren Run may not have sparked a candidacy, it ignited a movement."

By effectively pulling out, the Warren campaign (which, to be sure, never actually included Warren herself) is consolidating support behind the remaining candidates. Already, Kurt Ehrenberg, a veteran New Hampshire strategist previously in charge of Run Warren Run’s New Hampshire operation, has left the group to lead the Sanders effort in the Granite State.

As for "Run Warren Run," the movement will pivot away from working to draft Warren for president and toward pushing for her issues, like battling the Trans-Pacific Partnership.

But the Warren camp still isn't giving up on its leader. Another pro-Warren group, Ready for Warren, is still working to convince the senator to run.

And even "Run Warren Run," hasn't completely thrown in the towel.

As Ilya Sheyman, the executive director of MoveOn, wrote in his Politico opinion piece, "If she chooses to reconsider ... the movement that urged her to run could regroup at a moment’s notice."