With Book, Buchanan Set His Fate As the conservative polemicist Pat Buchanan prepared last fall for the release of his book "Suicide of a Superpower: Will America Survive to 2025?," some friends who worked with him at MSNBC were worried. The book, they told him, would provoke controversy and threaten his professional well-being. Undeterred, Mr. Buchanan began his book tour, but his friends were right. He stopped being asked to appear on shows on MSNBC, the cable news channel where he had been employed for nearly 10 years. On Feb. 16, the channel said in a brief statement: "We've parted ways with Pat Buchanan. Why was he pushed out? To Mr. Buchanan, 73, a white Catholic, his departure was a disappointing overreaction both to the book - which conveyed his long-held concerns about the effects of demographic changes in the United States - and to complaints about it by liberal advocacy groups. In the pessimistic book, he bemoaned that birthrate trends and "Third World" immigration were precipitating "the end of white America." At MSNBC, "there was apprehension that my book would cause some kind of explosion and firestorm, which it did not," Mr. Buchanan said by telephone on Saturday. To be honest, I've never had a better reception for a book I've written. To executives at MSNBC, however, the book's statements were indefensible and, though they did not say so publicly, incongruent with a channel that has branded itself as progressive and forward-thinking and has a disproportionately high share of African-American and Hispanic viewers. Though Phil Griffin, the president of MSNBC, denied that the channel's political identity was a consideration in the breakup, he said last week, "I want MSNBC to reflect America in the 21st century, not the America of the 1940s." As cable news channels like MSNBC and Fox News Channel have grown highly politicized, they have become arbiters of the bounds of acceptable discourse - not always a comfortable role for those involved. A corporate allergy to controversy sometimes exists, even though controversy is what sometimes motivates channels to hire commentators and compels people to watch. Timothy Stanley, a British historian whose biography of Mr. Buchanan, "The Crusader," was released two weeks ago, said he thought the departure was a "marketing decision" by MSNBC, a unit of Comcast. They took an opportunity to get rid of someone who was doing damage to their liberal brand. Mr. Buchanan has always been an ardent conservative. That's why he was hired by MSNBC in 2002, after spending the previous 20 years as host of CNN's "Crossfire" between unsuccessful runs for president. At that time, MSNBC called itself "fiercely independent" and had no clear political tilt. Though accused by some of hate and intolerance, Mr. Buchanan was, for a long time, the visible conservative commentator on MSNBC. He was well liked by colleagues at the channel, even by those with opposite views. "Nobody was more polite, gracious and charming," said David Shuster, who shared an office with him for several years and is now a substitute anchor for Current TV, a liberal competitor of MSNBC. Mr. Buchanan was paid well, too. By 2007, he was making more than $500,000 a year at MSNBC, the most of any commentator, according to past and present MSNBC employees who insisted on anonymity because contract details were confidential. The employees said his salary was high in part because he was co-anchor of a show in 2002 and 2003. And he was writing conservative calls to arms all the while. In 2002, it was "The Death of the West: How Dying Populations and Immigrant Invasions Imperil Our Country and Civilization;" in 2006, it was "State of Emergency: The Third World Invasion and Conquest of America." While the most recent book is "much more comprehensive," Mr. Buchanan said, "basically the theme is the same one."