Rep. Alexandria Ocasio-Cortez (D-N.Y.) watched Tuesday night's Democratic debate, and one thing stood out to her.

"Not a single climate change question," she tweeted. "Horrifying." One of the participants, Sen. Bernie Sanders (I-Vt.), agreed, responding, "A disgrace." The Democratic candidates don't shy away from talking about climate change on the campaign trail; billionaire investor and environmentalist Tom Steyer told voters in South Carolina on Tuesday that climate change is his "No. 1 priority," and if elected, he will declare a climate emergency on his first day in office.

Poll after poll has shown that climate change is a key issue for voters; last week, the Pew Research Center released a survey showing that for the first time in two decades, a majority of Americans believe that tackling climate change should be a main priority for the president and Congress.

Another poll released last week by the nonpartisan nonprofit Climate Nexus found that for Democrats, climate change is one of the two most important issues facing the country right now. "This is the first time in American political history where climate change is not just a top-tier issue, it is the top-tier issue," Anthony Leiserowitz, a senior research scientist at Yale who helped conduct the poll, told The Atlantic.

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