The impeachment trial begins with an argument about whether it is constitutional in the first place. And, how the Keystone XL pipeline became a political shorthand for climate policy. Read more:On the first day of former president Donald Trump’s second impeachment trial, his attorneys are asking: Can a president even be impeached after he has left office? Reporter Ann E. Marimow explains the constitutional questions at play.President Biden has said that addressing climate change is one of his foremost priorities as president. And since his first day in office, he has taken aim at controversial oil and gas policies, such as the previous administration’s support of the divisive Keystone XL pipeline. Senior national affairs reporter Juliet Eilperin on the future of pipelines in the United States. As the impeachment trial continues this week, consider going back to listen to our deep-dive into the events at the Capitol on Jan. 6. That episode gives a moment-by-moment breakdown of the riot, with voices you may not have heard before, and insight into the events at the center of the impeachment trial. That episode of Post Reports is called “Four Hours of Insurrection,” and you can find it here or wherever you get your podcasts.For the latest impeachment news, check out washingtonpost.com or The Daily 202’s Big Idea, a morning news briefing from The Washington Post. If you value the journalism you hear every weekday in this podcast, consider subscribing to The Post. You can find a special offer just for our listeners at postreports.com/offer.