Democratic presidential candidate Sen. Kamala Harris (D., Calif.) said the United States could afford trillion dollars of spending in the Green New Deal.

CNN host John King, in an interview that aired Sunday, spoke to Harris and asked about the realism behind the proposals dominating the nascent Democratic primary, which appears to be a race to the left among Harris and the other leading candidates.

"If you talk to Democratic voters, they're hungry and they want ideas. So you'll hear things like the Green New Deal. You'll hear things like ‘Medicare for all,' you hear things whether it's taxes … at what point do you say, ‘that's our north star but we have to be realists?'" King asked.

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

"Can we afford it?" King asked.

"Of course we can afford it," Harris said.

Rep. Alexandria Ocasio-Cortez (D., N.Y.), a proud democratic socialist, and Sen. Ed Markey (D., Mass.) released an outline of the Green New Deal earlier this month.

The resolution outlines numerous goals like providing every resident of the United States with a federal job that includes paid vacation and retirement benefits, "adequate housing," "healthy food," "Medicare for all," and "access to nature." The plan would also aim to achieve "net-zero greenhouse gas emissions through a fair and just transition for all communities and workers."

In an additional document released by Ocasio-Cortez's office, it suggested even more radical goals for the Green New Deal. The plan aims to replace every combustible engine, make air travel unnecessary, and retrofit or rebuild every building in the country to be more environmentally friendly.

"Totally overhaul transportation by massively expanding electric vehicle manufacturing, build charging stations everywhere, build out high-speed rail at a scale where air travel stops becoming necessary, create affordable public transit available to all, with goal to replace every combustion-engine vehicle," the document states.

Cost estimates for some of the provisions in the plan are in the range of trillions of dollars. Harris and other 2020 presidential candidates have lined up behind it, as well as "Medicare for all."

"Tw0-and-a-half trillion dollars, $3 trillion for ‘Medicare for all' by some studies. Depending on which portions of the Green New Deal you choose to do first, that's money. You know what Republicans are going to say, ‘tax and spend liberals, pie in the sky,'" King said.

Harris said the focus should not be about the cost of the plan but what the return on investment will be.

"It's not about a cost," Harris said. "It's about an investment. And 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?"