That CNN aired a seven-hour town hall last week on the climate crisis with 10 Democratic presidential candidates is a measure of the stunning sea change in the politics of climate change. In 2016, the media offered not one question on climate in the three general-election debates. Four years on, climate is already one of the defining issues of the campaign.

Its growing profile is a reflection of realism and of citizen activism. Fires in California and the Amazon, floods in the Midwest, savage storms along the Eastern Seaboard have awakened voters and the media to the clear and present danger that climate change poses. And citizen groups — exemplified by the young activists at the Sunrise Movement — have forced the demand for a bold Green New Deal into the political debate.

Thanks in part to grass-roots pressure, the vast majority of the Democratic presidential candidates have already put out climate plans. Virtually all agree that climate change represents both a present danger and, if unchecked, a threat to civilization as we know it. All agree that bold action is needed right now, and that government has to lead. Their plans vary dramatically in scope and ambition, but the commitment is universal.

In stark contrast, President Trump remains in denial of reality, has dismissed climate change as a hoax and has been eager to paint Democrats as socialists intent on sabotaging the economy. The right’s propaganda machine — led by Fox News — continues to peddle lies, painting the Green New Deal as a leftist crusade to ban meat and end air travel. No matter who the Democratic nominee is, Trump’s hostility to any action on the climate will likely remain key to the disgraceful, divisive and dishonest campaign he is already running.

The critical question, then, is whether the Democratic nominee is prepared to stand up and argue the case — or whether he or she will wilt against the Trump fusillade. Many establishment voices are already warning Democrats that anything bold enough to be a Green New Deal would be too extreme and perhaps be a gift to Trump. Not surprisingly, Sen. Bernie Sanders (I-Vt.), who put forth the boldest plan, has drawn the most fire. Sanders’s blueprint — which calls for spending $16 trillion over a decade to meet its goals, including moving to 100 percent renewable energy by 2030 — is dismissed by many as too radical, too costly, too ambitious and too politically dangerous. MSNBC analyst Jonathan Alter described Sanders’s plan as “pie-in-the-sky.” Christy Goldfuss, who worked on climate issues in the Obama administration, told The Post, “If Americans are scared that this is going to negatively impact their economy, they will not be supportive of the most ambitious climate plan and they won’t be supportive of the Democratic nominee.” Paul Starr, a liberal Princeton sociologist and co-founder of the American Prospect magazine, scorned the Sanders plan to CNN: “This is not what the country needs or is likely to support. On the climate issue, the first job of Democrats is to convince people that they have an achievable and realistic plan. The Sanders proposal won’t do that.”

No question Sanders’s plan is staggering in size and scope. The annual cost alone would exceed the military budget. But unrealistic? The scientific consensus is that we’ve got until 2030 to make massive cuts to carbon emissions to avoid truly catastrophic damage. Even then, we will suffer brutal climate calamities from the warming that is already taking place. As environmentalist Bill McKibben notes, Sanders’s plan actually tackles what is demanded by the threat.

Whether the plan is a political liability is also debatable. Trump will denounce it as Venezuela redux, and Fox News will claim it will commandeer your car, but they’ll react that way to any Democratic plan. Given the increasingly polarized electorate, it’s less important to appeal to the increasingly rare undecided voter than to mobilize one’s base. One key variable for Democrats will be the turnout of young voters. And on that front, there’s no question that young activists such as the Sunrise Movement are put off by “moderate” reforms inadequate to the existential challenge that they must face. Moreover, in an era when voters are understandably cynical about politicians, sympathetic voters are likely to be suspicious of candidates promising bold results from timid plans.

There is, of course, a big debate to be had about the elements of any plan. But Democrats would be wise to ignore much of the punditry’s pearl-clutching about being too bold or its cautions about moving to the middle. The climate catastrophe is real. The president is in denial, and Republicans are too cowed to break with him. This is a defining issue for which Democrats should stand up and fight.

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