Professor S. James Gates has spent his career pioneering modern physics and diversity in science. His most recent book, written with novelist Cathie Pelletier, is about how scientists proved Einstein's groundbreaking theory of relativity all those years ago. Walter sits down with Gates to find out just how they did this, and how his own upbringing played such a pivotal role in his success.

Extreme weather events are galvanizing a new climate conscious generation of consumers who are prepared to commit to sustainable lifestyles even if it means paying higher prices to do so. Allbirds, the company known for its seductively comfy wool shoes, helped drive this growing demand. The company's co-CEO Joey Zwillinger joins the program to discuss eco-friendly business practices.

As a climate scientist, educator, and lead author for U.S. national climate assessments, Katharine Hayhoe is devoted to exposing diverse—sometimes suspicious—audiences to the cataclysmic events happening right before our eyes as a result of climate change. She joins the program to explain how to convince people and what changes are needed.

Never in 50 years has Venice seen a catastrophe like this: historic storm waters have deluged the historic site three times in a single week. Six foot tides are engulfing 85% of Venice's streets and buildings, including the iconic St. Mark's Basilica. Henk Ovink is a world renowned expert on flooding, as a special water envoy to the United Nations, and joins the program to discuss this crisis.

Historian and journalist Rick Perlstein has been called the “chronicler extraordinaire of American conservativism,” and he has studied what the Nixon and Clinton scandals can tell us about today’s hearings. Perlstein sits down with Alison Stewart to provide a historical lens and some much-needed perspective to the ongoing impeachment hearings.

Marie Yovanovitch describes vital U.S. interests as trying to help set up a stable, free and democratic Ukraine that could resist pressure from Russia. New Yorker columnist Masha Gessen has deep insight into how authoritarian leaders like Vladimir Putin function, and says she is “shocked but not surprised” by what we are learning in this impeachment inquiry. She joins the program from New York.

Today, Marie Yovanovitch testified publicly in the impeachment inquiry against President Trump. James Melville, a career diplomat who knows her personally, can understand more than most what she has experienced – he himself quit as U.S. Ambassador to Estonia last year in protest over President Trump’s comments about European allies. He joins the program to assess Yovanovitch’s testimony.

It took the buy-in of Democratic representatives from swing districts to prompt Speaker Pelosi to begin the impeachment investigation. One of those was Democratic Congresswoman Elissa Slotkin, who has faced challenges convincing her constituents of the need to consider impeachment. She joins the program from Michigan to assess how the week’s hearings have gone down in her part of the country.

When Adam Frankel was 25 years old, he discovered something shocking: he wasn’t his father’s biological son, a secret his mother had kept from him his whole life. At the time, he was making waves as a talented speechwriter for President Obama. His debut book “The Survivors” captures his experience, and he sits down with Walter to discuss his powerful story.

Washington is gearing up for a second day of public impeachment hearings on Friday, when Marie Yovanovitch will testify. Nancy McEldowney was a colleague of Yovanovitch’s for many years, having served in the foreign service under both Republican and Democratic administrations; she joins the program with former FBI general counsel James Baker, who oversaw the launch of the Mueller investigation.

A new film starring Mark Ruffalo is a true story about cover-ups and conspiracies at the highest levels of the corporate world. “Dark Waters” follows Rob Bilott, played by Ruffalo, who took on the chemical company DuPont after one of its West Virginia plants leaked the chemical PFOA into the water supply. Ruffalo and Bilott join Christiane to discuss this true and timely investigation.

Today, Congress began hearing public testimony in the impeachment inquiry into President Trump. To digest this first day of public impeachment testimony, Christiane speaks with former representatives from both sides of the aisle: former chair of the House Intelligence Committee Mike Rogers and former member of the House Judiciary Committee Elizabeth Holtzman.

In today’s hearings, there was talk of President Trump trying to publicly box in President Zelensky, involving a planned TV interview where the Ukrainian leader was to publicly announce investigations into the Bidens and alleged Ukrainian meddling in 2016. To provide perspective on these tactics, Christiane speaks with veteran journalist Jeff Greenfield and legendary reporter Carl Bernstein.

At the heart of the impeachment inquiry is Ukraine, and today’s testimony brought into sharp relief the challenges that country faces both militarily and over corruption. To understand what’s at stake for Ukraine and why it is vital to US foreign policy interests, Anthony Gardner joins the program in London.

Garry Kasparov became the youngest world chess champion in history at the age of 22, while his famous matches against the IBM supercomputer Deep Blue brought chess and artificial intelligence into the mainstream. Now, he’s focusing on the quiet war Russia is waging against U.S. democracy. Kasparov sits down with Miles O’Brien to discuss everything from troll farms to election interference.

The impeachment inquiry is an inevitably political process, despite the non-partisan credentials of the witnesses scheduled this week. Joe Crowley was chair of the House Democratic Caucus until he lost his primary to Alexandria Ocasio Cortez, but remains close to House Speaker Nancy Pelosi. He joins the program in London to break down what we can expect politically from the coming hearings.

On Wednesday, the all-consuming political drama of impeachment goes public for the first time on Capitol Hill, with the chance to see testimony first-hand from various government officials – including Trump appointees – who have corroborated the original whistleblower complaint. Former Deputy CIA director John McLaughlin joins the program to discuss what's at stake.

In Israel today, many cities have closed schools and businesses as Palestinian militants fired missiles across the border. This comes as Israel languishes in a state of political confusion: after two inconclusive elections, Blue and White Party leader Benny Gantz is still trying to form a ruling coalition, after Prime Minister Netanyahu’s failed attempts. Yair Golan joins the program to discuss.

Ronan Farrow was at the forefront of the reporting that triggered the #MeToo movement, and shared a Pulitzer Prize for his efforts. Having helped expose allegations of sexual abuse by Hollywood mega-producer Harvey Weinstein, Farrow now goes further in his new book, “Catch and Kill.” He sits down with Michel to detail his painstaking investigations.

Artist Antony Gormley's newest exhibition represents a significant milestone in his career, as he takes over the prestigious Royal Academy in London with a series of experimental installations. Few other artists would be allowed to flood one room with water and mud, or drill holes in a glass dome in another space—but Gormley was. He gives Christiane a hands-on look at his work.