This week’s Democratic presidential debates are poised to showcase just how far left the party has moved in the last several years — especially on energy and climate change.

Why it matters: The Democrats’ eventual nominee is likely to be the most progressive in decades. Proposed policies could cripple oil and natural gas, direct trillions of dollars to renewable energy and reassert U.S. leadership abroad on climate change. It’s an open question whether most Americans would support them.

The big picture: The trend to embrace more progressive energy and climate policies is part of the Democratic Party’s broader leftward shift over the last decade on various issues. (Republicans have moved to the right, but this column isn’t about them. This one is).

The rise of the Green New Deal in the last eight months has accelerated and crystallized the Democratic Party’s leftward move. But that lofty proposal is an effect, not a cause of this shift, which has been underway for years.

Driving the news: Many of the Democratic presidential hopefuls support positions that were hardly emphasized in prior White House contests. Here are highlights, with much of the details courtesy of this Washington Post survey first published earlier this month.

Banning fossil fuel development on public lands . This has been a talking point among some environmental activists for years, but it’s never permeated high-level politics like it has already in this contest.

. This has been a talking point among some environmental activists for years, but it’s never permeated high-level politics like it has already in this contest. Supporting a price on carbon dioxide emissions . Hillary Clinton didn’t even include an explicit price on CO2 in her climate plan as the Democratic nominee in 2016. Yet today, not only are most candidates supporting one, it's not even enough by itself when they do to satisfy vocal and influential climate activists.

. Hillary Clinton didn’t even include an explicit price on CO2 in her climate plan as the Democratic nominee in 2016. Yet today, not only are most candidates supporting one, it's not even enough by itself when they do to satisfy vocal and influential climate activists. Setting goals of reducing U.S. greenhouse gas emissions to zero . The aggressive benchmark had been something like an 80% reduction by 2050. Now it’s definitely zero emissions by then, if not by 2030. (Many experts say such goals would be very difficult to meet).

. The aggressive benchmark had been something like an 80% reduction by 2050. Now it’s definitely zero emissions by then, if not by 2030. (Many experts say such goals would be very difficult to meet). Pledging not to take fossil-fuel campaign donations . Most candidates, including the front-runner Joe Biden, have pledged to sign the pledge. The pledge, run by several environmental groups including Oil Change U.S., has had a strong influence in just two years of existence.

. Most candidates, including the front-runner Joe Biden, have pledged to sign the pledge. The pledge, run by several environmental groups including Oil Change U.S., has had a strong influence in just two years of existence. Banning fracking. This has become far more commonplace in today’s progressive debates than ever before. Clinton, who supported the controversial oil and gas extraction process as secretary of state under Barack Obama, came close to backing a ban at a 2016 primary debate against Sen. Bernie Sanders, who has long opposed fracking.

The intrigue: The drivers of these shifts are many and interwoven. Including…

A stronger economy compared to the last few presidential contests.

Increasing urgency from scientists about climate change.

Growing concern for the environmental footprint of natural gas.

Plummeting costs of renewable energy.

These factors, combined with Trump in the White House dismissing climate change, have supercharged activists successfully pushing Democratic politicians to adopt ever-more aggressive goals in the face of inaction at federal and global levels.

“Climate change is a unique public policy issue, in that it gets harder to solve the longer you wait. Since we haven’t taken adequate steps to solve the problem, the tools to solve the problem by definition have to become bigger, more aggressive and with shorter time frames.”

— Jeff Navin, former Obama administration official who has advised Democratic candidates and lawmakers

What I’m watching (beyond the debates this week): Whether the progressive climate positions espoused by most of the Democratic candidates are generally embraced by voters.

As of January, climate change remains a low priority for Americans. It was second to last among a list of 20 priorities for Washington, according to a Pew Research survey from then.

A recent CNN poll suggests Democratic primary voters are far more concerned about climate change than past elections, but it’s not yet clear how broad such support goes beyond that subset.

There’s also what I’ve described as the big climate disconnect: More people around the world are saying they’re worried about climate change — but that concern is not translating into a willingness to pay more for energy or vote for candidates supporting aggressive action on the issue.

The bottom line: This presidential contest, both the Democrats’ primary fight and the general election, will be one of the clearest tests of people’s appetite to support aggressive climate policies.