President Trump wrapped up his visit to the World Economic Forum in Davos, Switzerland today, where the focus this year is on climate change. From the White House to Australia to Brazil, leaders still aren’t taking measurable action — even as their countries face catastrophic weather events. João Doria, governor of São Paulo, Brazil, joins the program from Davos to discuss this pressing issue.

Democrats and Republicans are laying out their opening arguments for and against the impeachment of Donald J. Trump, a process that will last several days in the Senate. Two former chiefs of staff from both sides of the aisle, Danny Weiss and Jonathan Burks, join Christiane to discuss why communication is not working between the two parties.

Russia may already be attempting to interfere in the 2020 presidential election, if reports that Moscow hacked into Ukrainian gas company Burisma prove correct. It’s the kind of attack that keeps John P. Carlin up at night; he was Assistant Attorney General for National Security and speaks with Hari about the ever-rising cyber threat.

On Capitol Hill today, 100 senators begin deciding whether to remove President Trump from office on charges of abuse of power and obstruction of Congress. To discuss the anatomy of the third impeachment trial in American history, Christiane is joined by Noah Feldman, one of the four legal scholars who testified before the House Judiciary Committee hearing on impeachment.

Renowned Nobel laureate Joseph Stiglitz joins the program from the World Economic Forum in Davos, Switzerland to discuss the economy, growth and the climate crisis.

Sarah Hurwitz was a White House speechwriter, first for President Barack Obama, then for First Lady Michelle Obama. Her new focus is a departure from politics, asking instead what Judaism can teach us in these divisive times. She tells Michel about her book “Here All Along” and waking up to the faith she was born into.

Contentious elections are nothing new and 1856 proved a particularly fraught example. In “Imperfect Union,” NPR host Steve Inskeep tells the story of America’s first political power couple, John and Jessie Fremont. He joins the show from D.C. to discuss their lives and assess parallels with today’s politics.

This week, in the Senate, President Trump’s impeachment trial starts in earnest. Russia experts Evelyn Farkas and Dimitri Simes join Christiane to analyze how this affects U.S. relations with Russia.

Dan Buettner is a National Geographic fellow and founder of The Blue Zones Project, a well-being improvement initiative launched in over 40 cities across the United States. It also inspired a cookbook called “The Blue Zones Kitchen,” based on the diet of people who live in these zones living long and healthy lives. Buettner tells Hari exactly what makes these places so special to him.

Father Greg Boyle is a Catholic priest and founder of Homeboy Industries, the largest rehabilitation program in the world for active gang members. Over 3-plus decades, Father Boyle has helped more than 15,000 people a year break their vicious cycles of violence, find jobs and leave gangs behind. Boyle tells Christiane about the healing power of tenderness and spirituality.

For more than 25 years, Peggy Orenstein broke new ground with her intimate explorations of girls and sexuality in New York Times bestsellers like “Girls and Sex.” Now she turns her eye to “Boys and Sex,” hearing directly from young men about their most intimate experiences. Christiane speaks with her about the pervasive messages our culture sends about emotional suppression and sexual aggression.

Henry Louis Gates, Jr. has explored the ancestry of dozens of people from diverse backgrounds on his show Finding Your Roots, including Christiane’s in 2019. Now in its sixth season, the show features guests like Jeff Goldblum, RuPaul, and Queen Latifah. Gates believes family tapestries can offer a sense of stability and joins Walter Isaacson to discuss what he's learned about race and identity.

Australian mining magnate Andrew Forrest is digging into his own pockets to donate $48 million to fire relief in his country. As the founder of Fortescue Metals Group, Forrest leads one of the world’s largest iron ore producers and has enormous political clout in Australia. He joins Christiane to discuss his views on climate change.

In an exclusive interview, Ukraine’s foreign minister says he doesn’t know or trust Lev Parnas, an associate of Rudy Giuliani, who gave an explosive interview detailing the White House’s efforts to intimidate the Ukrainian president into providing information about Joe Biden. Christiane spoke with Vadym Prystaiko in London, where he was to attend a meeting about the downing of the Ukrainian plane.

French philosopher and writer Bernard-Henri Lévy has gone to the front lines of the fight against ISIS alongside Kurdish fighters. In two documentaries, Peshmerga and The Battle of Mosul, he tells the story of a people repeatedly abandoned by the West, who continue to fight for shared causes and values. Lévy tells Hari about his projects and explains how he has evidence ISIS is regrouping.

Prince Harry and Meghan Markle’s retirement as senior royals is still top news. But the couple has always been open about their struggle with being tabloid fodder. So, less than two years since their fairy-tale wedding, what's changed? Could the move provide a way forward for an increasingly irrelevant royal family? Journalist Afua Hirsch and royal historian Robert Lacey join Christiane to assess.

Last night, the six Democratic candidates faced off in a debate for the final time before the Iowa caucuses next month. The party is split between two strands, moderates and progressives, but which stands a better chance of prevailing in November? Jennifer Granholm and Andrew Gillum have both represented key swing states for the Democrats, and join the program to discuss.

The Iranian government's lie about the Ukrainian passenger plane fits in with a global dilemma: how to navigate a post-truth world. Michel Martin delves into that conundrum with Lee McIntyre, whose book, Post-Truth, traces the development of this phenomenon from its roots in science denial, cognitive bias and postmodernism through the rise of “fake news,” and “information silos.

Gretchen Carlson was an anchor at Fox News and was the first to sue Fox CEO Roger Ailes for sexual harassment. Her case was eventually settled for $20 million, but this came with a mandatory non-disclosure agreement. Now, along with two other women who sued Fox, Carlson has launched “Lift Our Voices” to try and end the silence imposed by non-disclosure agreements.

Harvey Weinstein's career came crashing down after journalists Jodi Kantor and Meghan Twohey published their bombshell investigation, exposing alleged abuse and intimidation over decades. They told the story of their own reporting in the recent book “She Said”, and Kantor speaks with Christiane from the New York Times office to give an update on the Weinstein story.