At the marathon climate-crisis town hall, about half of the 10 Democratic candidates participating embraced attaching a fee, or tax, on carbon dioxide pollution.

It’s a tack that proponents argue is the most effective way to significantly cut emissions. It’s also an approach that even some Democrats say is a political liability.

The fee can be spun as an energy tax that could raise fuel costs for businesses, and by trickle down, consumers. How aggressively businesses are charged is grist for future debates, as is analysis of the short-run versus long-run economic impact of pollution. Mother Jones blogger Kevin Drum, for instance, flags current policy iterations of carbon penalties as a regressive tax that disproportionately burdens lower-income households.

Read:Climate change, and how to combat it, takes center stage at Democratic candidates’ forums

Climate-focused candidate Gov. Jay Inslee is now out of the presidential race and most remaining candidates had not featured an explicit carbon price in their proposals, instead choosing emissions targets as a means of stopping ozone depletion.

But now, broadening candidate support for the fee is a change from the 2016 campaign, when Hillary Clinton kept clear of embracing a price on pollution for fear it would be attacked as an energy tax. The 2016 victor Donald Trump has rolled back regulations curbing emissions and withdrew from the global Paris agreement to address the climate crisis, citing lax adherence by China, India and other developing nations.

On Wednesday night, Sen. Elizabeth Warren answered ”Yeah” when asked by CNN moderator Chris Cuomo if she would support a carbon tax. It was a policy point she had not yet spelled out in her official proposal.

Read:Where the 2020 Democrats stand on climate change

“I think of this as what my mother taught me, and that is you’ve got to clean up your own messes and that means if you’re going to be spewing carbon into the air and messing up the air for the rest of us, it’s your responsibility to clean it up, and we’ve been talking about this for a long time. We’ve actually started putting parts of this in place in New England and other regional areas,” Warren of Massachusetts said.

“But, yes, we need to say that those who are throwing the carbon into the air, that the rest of us have to breathe, that the rest of us have to deal with, are the ones who are responsible for paying for that,” she added.

Former Vice President Joe Biden also expressed his support of a carbon fee with limited details, and so did Sen. Kamala Harris of California in her release ahead of the town hall. With this and other steps, Harris’s plan aims to reduce greenhouse gas emissions to zero by 2045, five years faster than the target of the Green New Deal framework championed by progressive Democrats.

Sen. Bernie Sanders has put a $16.3 trillion price tag over 15 years on his broad climate plan, one of the most expensive, but he is one of the few leading candidates who has not called for a carbon tax.

Candidates that favor a carbon price do generally have less developed policies than those who follow a Green New Deal approach, says James Lucier, who leads the energy, environmental and tax practices at Capital Alpha, in a recent research note. Still, a majority of candidates are at least open to a carbon price, noted Lucier.

Mayor Pete Buttigieg of South Bend, Ind., who also released his climate plan on Wednesday, declared his support for a carbon tax Wednesday night, adding, “I know that you’re not supposed use the T-word in politics.”

Read:Number of young Republicans concerned about environment jumps in last five years

Republicans think the Democrats’ shift could be an “anti-tax” political opportunity. Conservative site Breitbart was featuring a series of video clips from the town hall, attaching a “carbon tax” label to the candidates who went on record Wednesday.

Candidate and tech-influencer Andrew Yang, for instance, starts his carbon-price proposal at $40/ton and gradually increases it to $100/ton. That equates to a gasoline tax of about 36 cents per gallon, rising over time to 88 cents per gallon. Drum, writing for Mother Jones, says the increase isn’t as sharp as consumers might think given the way elastic oil and gasoline markets already swing with market whims. That means, he writes, that an effective penalty might have to be larger than is politically palatable, or only made palatable by giving discounts to many households. And then, its effectiveness might not have the desired outcome.

“The whole point of a carbon tax is to make energy more expensive so that people will use less of it. But if you just give the money back, it means people can use their dividend to partially offset that higher cost. They can go on using the same amount of energy as always with minimal pain,” wrote Drum, who concedes a shift over the past decade away from a position in favor of carbon tax plans.

Opinion: Stopping climate change will be easier and cheaper than Democrats think, writes Tim Mullaney

A carbon tax, and many of the climate-focused reforms taking shape among the Democrats, likely face a filibuster roadblock, although that depends on the broader outcome of the 2020 congressional races. If the Senate remains in Republican hands, the filibuster is seen as the biggest hurdle to passing a comprehensive climate law. Thus, candidates were asked Wednesday if they approve scrapping the filibuster, which forces a 60-vote supermajority to end Senate debate.

Harris made news by saying she’d support ending the filibuster if Republicans stood in the way of a Green New Deal. Warren is so far the only other major candidate to voice support for ending the filibuster.