Despite the cascade of other crises this year, climate change has emerged as a key election issue. Two-thirds of Americans want the government to do more about it, and the same share of Biden supporters say it's very important to their vote. While not many Trump supporters overall agree, there's more concern among younger Republicans. The stakes are high as more Americans experience record heat, wildfires, hurricanes and flooding, and the two candidates could not be further apart. Joe Biden calls climate change an existential threat to our health, economy and national security. President Trump continues to question climate science. Here are six takeaways from Trump's first term on climate and energy, and the challenges he or Biden would face if elected.