U.S. Sen. Bernie Sanders stopped by the Late Show With Stephen Colbert to promote his new book, It’s OK To Be Angry About Capitalism.

The Vermont independent’s book, co-written with John Nichols and published Tuesday by Crown, argues that unchecked capitalism is creating a huge wealth gap and threatening the future of the country. A critic for Kirkus wrote of the book, “Even if they’re pie-in-the-sky exercises, Sanders’ pitched arguments bear consideration by nonbillionaires.”

Colbert asked Sanders about the recent train derailment in East Palestine, Ohio, which caused toxic chemicals to be released into the air, noting that railroad companies had successfully lobbied the Trump administration to roll back regulations on rail transportation.

“This is what the book is about,” Sanders replied. “We have a corrupt political system in which big money buys elections. Billionaires right now, through super PACs, can spend as much as money as they want, tens of millions, hundreds of millions of dollars to candidates who they want to represent their interests.”

Colbert noted that in his book, Sanders writes that the country needs a “new sense of morality.”

“Is it acceptable that we have, in the richest country on Earth, the highest rate of childhood poverty?” Sanders said. “Is it acceptable that today you’ve got three people on top who own more wealth than the bottom half of American society, and we have more income and wealth inequality today than probably ever in American history?”

Michael Schaub, a journalist and regular contributor to NPR, lives near Austin, Texas.