The Green New Deal has emerged as a key litmus test for prospective 2020 presidential candidates, with high-profile candidates jumping on board to back the progressive environmental pitch.

On Sunday, Sen. Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.) entered the 2020 race after supporting the proposal. Four other senators who have declared presidential bids have co-sponsored the resolution, and Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.), who is mulling a 2020 campaign and has previously supported the concept, will back the plan.

Their support highlights one of the progressive ideas at the center of the Democratic race, while the Republican National Committee dismissed the proposal as a "massive taxpayer boondoggle and a socialist dream come true."

Rep. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezHouse passes bill to avert shutdown Trump attacks Omar for criticizing US: 'How did you do where you came from?' The Memo: Dems face balancing act on SCOTUS fight MORE (D-N.Y.) and Sen. Ed Markey Edward (Ed) John MarkeySchumer: 'Nothing is off the table' if GOP moves forward with Ginsburg replacement Democrats see fundraising spike following Ginsburg death Democratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy MORE (D-Mass.) introduced a resolution last week that would lay the groundwork for implementing the Green New Deal legislatively.

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The resolution calls for the United States to achieve net-zero greenhouse gas emissions within 10 years, and a host of other environmental changes less directly related to climate change including support for family farming and investments in high-speed railroads.

Some have expressed skepticism about its chances of success or put caveats on their support. Speaker Nancy Pelosi Nancy PelosiPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare House lawmakers reach deal to avert shutdown Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE (D-Calif.) referred to the proposal as the "Green dream, or whatever they call it," and former New York City Mayor Michael Bloomberg (D) stressed that a Green New Deal should offer realistic solutions and not "things that are pie in the sky." Bloomberg is considering a 2020 bid, and has long been an advocate of combating climate change.

Former Texas Rep. Beto O'Rourke Beto O'RourkeJimmy Carter says his son smoked pot with Willie Nelson on White House roof O'Rourke endorses Kennedy for Senate: 'A champion for the values we're most proud of' 2020 Democrats do convention Zoom call MORE (D), who has said he will decide soon on a 2020 bid, last month expressed support for the "concept" of a Green New Deal.

Here's where most declared candidates for the 2020 nomination stand on the Green New Deal:

Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE:

Sen. Kamala Harris (D-Calif.) co-sponsored the Green New Deal resolution, which she touted as a "bold plan" to address an "existential threat to our nation."

The Green New Deal is a bold plan to shift our country to 100% clean and renewable energy. We do not fight this fight for our generation alone but for generations to come.https://t.co/Mzi2Y2LZg0 — Kamala Harris (@KamalaHarris) February 8, 2019

The California senator laid out her support for the proposal in a blog post last week on Medium, where she called the proposal a "bold plan," and pressed the need to "aggressively tackle climate change which poses an existential threat to our nation."

"Bold action takes bold leadership, and I’m grateful to Representative Alexandria Ocasio-Cortez and Senator Ed Markey for leading the charge on this critical resolution," Harris wrote.

Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE:

Sen. Elizabeth Warren (D-Mass.), who on Saturday officially declared her candidacy for president weeks after forming an exploratory committee, signed on as a co-sponsor of the Green New Deal after her office initially said she supported the "idea" of such a proposal.

"Climate change is real, it threatens all of us, & we have no time to waste to address it head-on," the Massachusetts senator tweeted in sharing her support for the resolution.

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She listed the Green New Deal alongside other progressive proposals she supports, including "Medicare for all," student loan relief and overturning Citizens United.

Warren has tied in her support for the Green New Deal to another of her most progressive proposals, an “ultra-millionaire tax,” that would apply to the wealthiest Americans.

She suggested in a tweet earlier this month that revenue from such a tax could go toward a down payment on the Green New Deal, or other proposals like Medicare for all.

With the revenue from the #UltraMillionaireTax, we could provide universal childcare for working parents across America. A path to student debt relief for those who need it. Down payments on a Green New Deal & Medicare for All. Schultz might not need those things. America does. — Elizabeth Warren (@ewarren) February 4, 2019

Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE:

Sen. Cory Booker (D-N.J.) is another Senate co-sponsor of the Green New Deal, and made his support for the measure clear during a recent campaign stop in Iowa.

The New Jersey senator shared a video on Twitter of a voter asking about the proposal and his explanation of the need for imminent action to address climate change.

"Doing nothing is not an option right now because our planet really is in peril," Booker said.

"So the question is, what’s the United States of America going to do?" he continued. "Is it going to lead the planet in terms of dealing with this crisis? Or is it going to pull back from global leadership when we are the biggest economy on the planet Earth?"

"I believe that America should lead, and it should lead boldly," he continued, calling the Green New Deal a "bold idea" that would benefit the environment and the economy.

The first question I was asked in Iowa was about #GreenNewDeal. The hard truth is climate change has imperiled our planet—it’s going to take bold action now to save it including dramatic investment in green energy that will create the jobs of the future. We can do this. pic.twitter.com/zdU26AjcNN — Cory Booker (@CoryBooker) February 8, 2019

Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE:

Sen. Kirsten Gillibrand (D-N.Y.) co-sponsored the Green New Deal, but had made clear her support for the idea roughly two weeks before it was formally introduced.

“The way I see a green economy is this: I think we need a moonshot," the New York senator told Pod Save America late last month. "We need to tell the American people ‘we are going to have a green economy in the next 10 years, not because it’s easy, but because it’s hard, because it’s a measure of our innovation and effectiveness.' "

Gillibrand also said on the liberal podcast that she supports putting a tax on carbon, likely through something similar to a carbon tax or cap-and-trade.

There's nothing left to debate. Climate change is an immediate and catastrophic threat to our future.



It's time for bold action, now. We need a #GreenNewDeal. https://t.co/YpVK11VGEK — Kirsten Gillibrand (@SenGillibrand) February 5, 2019

Amy Klobuchar:

The Minnesota senator on Sunday became the latest Democrat to officially join the field of presidential candidates, launching her campaign from snowy Minneapolis.

A spokesperson for Klobuchar told The Associated Press last week that she would sign on to support the Green New Deal. While the senator made no mention of the specific proposal in her speech on Sunday, she emphasized her commitment to environmentally friendly policies.

Klobuchar vowed to "put forth sweeping legislation to invest in green jobs and infrastructure" if elected president, and declared that she would direct the U.S. to rejoin the Paris climate accord "on day one" of her administration.

Julián Castro:

Julián Castro, the former mayor of San Antonio and an ex-Housing and Urban Development secretary, has yet to publicly weigh in on the Green New Deal since the resolution was announced late last week.

However, he has been a proponent of the concept since he first announced his White House bid.

"As President, my first executive order will recommit the United States to the Paris climate accord," he said on Jan. 12. "We’re gonna say no to subsidizing big oil and say yes to passing a Green New Deal.”

Castro has embraced a number of other progressive policy positions, including Medicare for all and "tuition-free" public colleges.

Tulsi Gabbard Tulsi GabbardRepublicans call on DOJ to investigate Netflix over 'Cuties' film Hispanic Caucus campaign arm endorses slate of non-Hispanic candidates Gabbard says she 'was not invited to participate in any way' in Democratic convention MORE:

Rep. Tulsi Gabbard (D-Hawaii) has not offered a specific position on the Green New Deal resolution, but has a track record of backing environmentally friendly policies that address climate change.

She introduced legislation in the last Congress that would have required 100 percent of electricity to be generated by clean sources by 2035.

In a tweet last month, Gabbard said the country needs "a green economy that rewards clean energy industries & ensures access to fresh, affordable, pesticide-free foods for all."

Gabbard's campaign did not respond to a request for comment on her views on the Green New Deal.

Pete Buttigieg

Pete Buttigieg on Sunday emerged as the latest Democratic presidential hopeful to offer his support for the Green New Deal, calling it "the right beginning" and a framework for addressing climate change.

"Obviously, the Green New Deal, as we have seen it so far, is more of a plan than it is a fully articulated set of policies," the Indiana mayor said on CNN. "But the idea that we need to race toward that goal and that we should do it in a way that enhances the economic justice and the level of economic opportunity in our country, I believe that's exactly the right direction to be going in."

Buttigieg noted that he's seen the effects of climate change firsthand as mayor of South Bend, Ind., which experienced historic floods in recent years. He argued the Green New Deal could simultaneously address the environmental and economic impacts of the changing climate.

"I think the elegance from a policy perspective of the concept of the Green New Deal is, it matches a sense of urgency about that problem of climate change with a sense of opportunity around what the solutions might represent," he said.

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Former Maryland Rep. John Delaney (D) said in a statement that the candidate supports "the energy behind the Green New Deal," but not the resolution itself.

"I prefer a more specific, actionable plan to do something big on climate, like the bipartisan carbon tax dividend bill I lead," Delaney said in a statement to The Hill. "We can't turn climate into a political issue, we need to do something big as soon as possible."

Delaney said last month that any big undertaking on the environment should feature a carbon tax at its center.

“As Democrats and climate advocates, we can’t turn this into an effort to move the goalposts," the former Maryland congressman in a statement. "We need to unite behind a solution that will work and a solution that can win the support of a broad coalition – that’s what we’re going to need to take a big step forward. A carbon tax should be the centerpiece of the Green New Deal.”

Updated Feb. 11 at 8:39 a.m.