By Ramesh Ponnuru

Bloomberg News

Much has been made of the willingness of Democratic presidential candidates to risk taking positions that aren’t popular with voters at large in order to boost themselves in the primaries. Democratic politicians and strategists are aware that most people don’t want to see private health insurance banned, for example, but such leading contenders as Senators Elizabeth Warren and Bernie Sanders have come out for it anyway.

There has been less focus on the political risks of the candidates’ approach to climate change. In part that’s because so many Republicans have taken their own unpopular stance on the issue: denying that there’s a problem. Gallup finds that nearly two-thirds of voters believe that human activity is causing the globe to get warmer, and that percentage has been rising over the years. Young voters are especially concerned about the issue. It’s part of the reason that some Republicans, such as Representative Matt Gaetz of Florida, have broken with many of their colleagues on the matter. “I think history will judge very harshly those who are climate deniers,” he said.

But the Democrats may be getting overconfident. At last week’s “climate town hall” on CNN, Senator Warren, former Vice President Joe Biden, and South Bend, Indiana, Mayor Pete Buttigieg all endorsed a carbon tax. Senator Kamala Harris did, too, although she called her tax a “fee.” All of these candidates are breaking with past Democrats. Neither President Barack Obama nor Hillary Clinton endorsed a carbon tax. A memo for the Clinton campaign estimated that a carbon tax of $42 per ton on greenhouse-gas emissions would raise annual energy costs by $478 for the average household, and by $268 for the poorest fifth of households.

When considering that number, keep in mind another poll finding. In November 2018, the AP-NORC Center for Public Affairs Research ran a survey about climate change that found, in line with other polls, that most Americans believe it is happening and that human activity is causing it. Nearly half of respondents said that recent extreme weather events had influenced their thinking on the issue. But 68 percent opposed paying even $10 extra in their monthly utility bills to address the issue.

The Clinton campaign’s memo also noted that the revenues from the tax could be rebated so that only the highest-earning fifth of households ended up with a net tax increase. But this should be less reassuring to Democrats than it appears. For one thing, several of the candidates either aren’t promising to rebate the taxes or aren’t emphasizing the point to deflect the inevitable attack on them. When asked about carbon taxes, Warren and Biden didn’t say they would have a rebate. Harris said that some of the money would go “to empower those communities that for too long have been ignored,” which doesn’t sound like a tax rebate.

Even a tax increase on the top fifth of households is a heavier political lift than Democrats have been prepared for. A household with an annual income of $130,000 is in that fifth. The tax increases of the last two Democratic presidents kicked in at a much higher threshold. And the gross cost may matter politically, not just the net cost. Even if the Democrats promise a rebate, Republicans can sow doubt that voters will actually see one.

Washington State’s relatively liberal electorate has rejected carbon taxes twice in recent years. In 2016, a carbon tax was paired with a sales-tax cut and drew the opposition of 59% of voters. In 2018, on a generally good day for liberal causes, 56% opposed a carbon tax with no rebate.

You can approve or disapprove with the public’s low tolerance for higher costs in the fight against global warming. (I myself favor lower-cost alternatives to carbon taxes.) But even those who consider it shortsighted have to reckon with it. Resistance to the costs of taxes and regulations is likely to be a bigger obstacle to climate plans, in the end, than disbelief in global warming.

The journalists at Vox did one of those round-ups of who won and lost from the climate town halls. (Winner: CNN; loser: meat.) But they ignored someone who might turn out to be the biggest winner: President Donald Trump, who will surely hit the cost issue hard as we get closer to the election.

Ramesh Ponnuru is a Bloomberg Opinion columnist. He is a senior editor at National Review, visiting fellow at the American Enterprise Institute and contributor to CBS News.