Democratic presidential hopeful Kamala Harris pointedly declined in an interview broadcast Sunday to put a price tag on the Green New Deal and "Medicare-for-all," which she has endorsed wholeheartedly even as Republicans cite nonpartisan cost estimates of trillions of dollars for each unprecedented proposal.

Harris, D-Calif., joined Sens. Elizabeth Warren, D-Mass., and Cory Booker, D-N.J. to co-sponsor the Green New Deal resolution earlier this month. The resolution's botched rollout included the release of an official document by New York Rep. Alexandria Ocasio-Cortez's office that promised economic security even for those "unwilling to work," as well as the elimination of "farting cows" and air travel.

"There's no question we have to be practical. But being practical also recognizes that climate change is an existential threat to us as human beings," Harris began. "Being practical recognizes that greenhouse gas emissions are threat to our air, and threatening our planet. And that it is well within our capacity as human beings to change our behaviors in a way that we can reduce its effect. That's practical. Of course we can afford it."

CNN's John King asked Harris for her response to conservative arguments that progressive proposals could end up doing more harm than good, by crippling the U.S. economy even as major polluters like China continue unabated.

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According to the Mercatus Center at George Washington University, for example, Ocasio-Cortez's plan for universal Medicare would end up costing more than $30 trillion, even after factoring in the sweeping tax hikes that would offset the expense by only roughly $2 trillion. Charles Blahous, a senior strategist at the Mercatus Center and an author of the study, later charged that Ocasio-Cortez had wildly misinterpreted his study to try to argue that "Medicare-for-all" would save money.

"One of the things that I admire and respect is the measurement that is captured in three letters: ROI," Harris responded. "What's the return on investment? People in the private sector understand this really well. It's not about a cost. It's about an investment. And then the question should be, is it worth the cost in terms of the investment potential? Are we going to get back more than we put in?"

Harris' loose invocation of an economics term echoed language by Ocasio-Cortez, who has repeatedly and confidently said "there's a little thing in economics known as externalities" to justify her Green New Deal proposal.

The Green New Deal push has seen resistance not only from Republicans, but also some key Democrats. Sen. Mazie Hirono, D-Hawaii, was asked about the plan to replace planes with high-speed rail and did not seem impressed.

“That would be pretty hard for Hawaii,” she laughed.

House Speaker Nancy Pelosi similarly appeared to dismiss the plan.

“It will be one of several or maybe many suggestions that we receive,” Pelosi told Politico. “The green dream, or whatever they call it, nobody knows what it is, but they’re for it, right?”

"It's not about a cost. It's about an investment." — 2020 Democratic presidential candidate Kamala Harris

Other Democratic presidential hopefuls, including Minnesota Sen. Amy Klobuchar, have cautioned that the Green New Deal resolution is merely "aspirational" and will likely need to be scaled back.

"The Green New Deal? I see it as aspirational. I see it as a jump-start," Klobuchar said on "Special Report with Bret Baier" earlier this month. "So I would vote yes [on the Green New Deal resolution], but I would also -- if it got down to the nitty-gritty of an actual legislation, as opposed to, 'Oh, here's some goals we have' -- uh, that would be different for me."

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But Harris said she was looking forward to hashing out the dispute with her rivals in public, during one of the 12 planned Democratic primary debates.

"I look forward to that debate on the debate stage," Harris said. "I look forward to it very much."

Meanwhile, the White House is angling for socialism to become the defining issue in the 2020 debate, amid Democrats' evolving vows for higher minimum wages and a new array of costly, universal benefits.

Speaking in a major foreign policy address in Miami to members of the Venezuelan community, President Trump declared Monday that "a new day is coming in Latin America" and issued a stark assessment that "socialism is dying" across the world. The address was the second time Trump publicly and forcefully has condemned what he has called "the horrors of socialism and communism" and "massive wealth confiscation" in recent weeks, following his similar vow during the State of the Union address that "America will never be a Socialist country."

But before Trump takes on the eventual nominee head-to-head, Democratic Party leaders acknowledged some internal divisions need to be resolved. Harris joined Warren this week in saying she supports taxpayer-funded reparations for black Americans affected by slavery, a stance that Democratic National Committee Chairman Tom Perez told "Fox News Sunday" was not officially endorsed by the party and would need to be hashed out during the debates as well.

In the meantime, Harris emphasized that her main concern is the concerns of everyday Americans.

"I'm hearing people in the state of Iowa, New Hampshire, South Carolina -- wherever you want to, name the state. Wisconsin, Michigan, I've been to those places too," Harris said, drawing a pointed contrast with Hillary Clinton, who did not visit Wisconsin following the 2016 Democratic National Convention and ended up losing the state to now-President Trump. "What they want to know is that people who want to be the leaders of this country are actually seeing them and thinking about the issues that keep them up at night."

But labor leaders -- who represent typically Democrat-leaning rank-and-file constituents -- have pushed back in recent weeks against the Green New Deal, saying its call for a total economic transformation could lead to widespread poverty.

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Speaking to Reuters, a spokesman for the coal industry union United Mine Workers (UMWA) specifically took umbrage at the Green New Deal's resolution's call for a "fair and just transition for all communities and workers" in order to "achieve net-zero greenhouse gas emissions" in the span of just ten years.

“We’ve heard words like ‘just transition’ before, but what does that really mean?" the spokesman, Phil Smith, said in an interview. "Our members are worried about putting food on the table."

Even aside from the Green New Deal, conservative commentators have argued that most proposed solutions to global warming would do more harm than good, and also have accused climate activists of crying wolf. In 2006, a NASA scientist and leading global warming researcher declared that the world had only 10 years to avert a climate catastrophe -- a deadline that has come and gone.