Kamala Harris on Monday became the latest Democratic presidential contender to back a Green New Deal, in what has become a "litmus test" for 2020 hopefuls, according to the youth-led Sunrise Movement that helped launch the ambitious economic and climate proposal.

"I support a Green New Deal and I will tell you why," the California Senator said during a CNN town hall in Iowa. "Climate change is an existential threat and we have got to deal with the reality of it."