Last November, the “Green New Deal” was barely on the lips of any Democrat running for office.

Fast-forward two months, and the phrase is all over the campaign trail.

Potential presidential candidates who otherwise have starkly different political approaches — from Sen. Bernie Sanders (I-Vt.) to former New York mayor Michael Bloomberg — are talking in increasingly positive terms about forging a deal to curb climate-warming emissions.

But right now, “Green New Deal” is a just slogan. Presidential hopefuls want to appeal to the Democratic Party’s progressive base, but they appear hesitant to bind themselves yet to any specific policy proposals — or outline what might constitute this kind of landmark climate deal.

An aide to Sen. Elizabeth Warren, for example, recently told the online news outlet Axios that the Massachusetts Democrat supports the “idea” of a Green New Deal.

Sen. Kirsten Gillibrand (D-N.Y.), who like Warren has already declared her candidacy for president, recently said on the left-leaning podcast “Pod Save America” that “the platform of it is really exciting," even through “there’s not a lot of details yet behind the Green New Deal.”

Bloomberg, who is mulling a White House bid, offered a caveat during a speech in New Hampshire on Tuesday: He told an audience that he wants an “achievable” Green New Deal.

“I’m a little bit tired of listening to things that are pie in the sky that we never are going to pass, are never going to afford,” he added.

An ambitious platform seeking to combat climate change is being championed by progressives like Rep. Alexandria Ocasio Cortez (D-N.Y.). (Adriana Usero/The Washington Post)

Those less-than-full-throated endorsements hint at a coming tussle over the exact meaning of what has become a popular rallying cry among Democrats. The question now is: Will the eventual Democratic nominee end up on the same page as the Democratic base when it comes time to forge such a deal?

Many progressive activists are looking toward an ambitious proposal put forward by freshman Rep. Alexandria Ocasio-Cortez (D-N.Y.), who outlined her vision for a Green New Deal after her election. She wants Congress to pass legislation that would rapidly transform the U.S. economy — including getting 100 percent of the nation’s electricity from “clean” sources while guaranteeing a job for every American to facilitate that transition.

As the idea of a Green New Deal gains steam beyond the far left, progressive activists want to see Democrats stay true to these core ideas.

“These are still politicians, and they can spot a winning idea when they see one,” said Stephen O’Hanlon, a spokesman for the Sunrise Movement. That youth-led activist organization thrust that catchphrase into the political conversation in Washington by twice storming the office of Rep. Nancy Pelosi (Calif.), the leading House Democrat, last year.

But if Ocasio-Cortez’s and Sunrise’s climate goals “aren’t part of their vision for a Green New Deal, then it’s not a Green New Deal," O’Hanlon added.

But those goals, historically, are much more than congressional Democrats have been willing to stomach. Only a handful of presidential candidates have taken any action in Congress toward such ambitious moves to reduce carbon emissions — usually falling short of Sunrise’s goal of moving the country off fossil fuels by 2030.

For instance, Rep. Tulsi Gabbard (D-Hawaii), a long-shot White House hopeful, introduced a bill in the last Congress requiring 100 percent of electricity to be generated from clean sources by 2035. And Gillibrand has urged the Senate Environment and Public Works Committee to consider legislation to get the United States to net-zero carbon emissions “by as close to 2050 as possible.”

The field of 2020 presidential contenders are up against a unique set of challenges, from standing out on the campaign trail to dealing with President Trump. (Jenny Starrs/The Washington Post)

Still, establishment Democrats like Paul Bledsoe, an adviser at the Progressive Policy Institute who worked on climate change under President Bill Clinton, cautioned White House hopefuls against making vows they cannot keep.

“The Democratic presidential candidates want to embrace the energy and enthusiasm of the activists without promising next-to-impossible goals,” Bledsoe said. “So they are naturally hedging.”

So far, Ocasio-Cortez and some other new House members who have pressed Democratic leaders to establish a select committee to create detailed Green New Deal legislation have faced some setbacks. While Pelosi has created the special climate panel, she has allowed lawmakers who have taken money from fossil fuel companies to join it — over the demands of activists.

Nonetheless, this new crop of progressive lawmakers has succeeded at popularizing the idea among voters. A poll in December from Yale and George Mason University found that 81 percent of them either strongly or somewhat supported a “Green New Deal” when it was described to them.