WASHINGTON (CNN) -- After spending more than 30 years consulting for Democratic candidates, campaign operative Robert Shrum is using his pen to advance his own, liberal views."The book is about what I have seen the direction of progressive politics take, what happens to it and where I think it ought to go," Shrum told CNN in an interview.The veteran political operative was coy about what else he would say in his book, and Washington insiders were aflutter Wednesday about whether it would include sharp critiques of his clients and colleagues from past campaigns -- particularly the failed presidential bids of Sen. John Kerry and former Vice President Al Gore.Shrum did tell CNN he would not disparage Kerry or Gore but left open the door regarding criticizing his own party."I think we should wait for the book," Shrum said. "As long as people who in my view are attacking the Kerry campaign want to worry, I will just let them keep on worrying."Some of his critics are former Kerry colleagues, and they claim Shrum has not shouldered enough blame for the Massachusetts Democrat's unsuccessful attempt to defeat President Bush in 2004. In January, Shrum credited Bush aide Karl Rove with doing "a very good job of coming up with a plan to mobilize Republican voters," but he played down the importance of campaign advisers."I think it's always a mistake to believe that the people who do what I do are the drivers of this, rather than the candidates," he said. "In the end, it's the candidates."One former Kerry campaign staffer said Shrum wrongly consolidated power by simultaneously acting as media strategist and political strategist."He was a disruptive force on the campaign," said the staffer, who spoke on the condition of anonymity. "Not nearly enough of that story has been told."Other Democrats, though, said Shrum might be able to provide some insight on how to revive the party's prospects. He has been a force in Democratic politics for three decades and has worked on eight presidential campaigns as well as countless congressional, gubernatorial and international races.While Shrum achieved success in congressional races, he never won a presidential contest for his clients."Shrum is a fabulous writer and a very intelligent person," said Anita Dunn, a Democratic media consultant. "He can potentially shed an interesting point of view on the Democratic Party during a time of great transition."Erik Smith, another veteran Democratic operative, suggested the book likely would shape Shrum's future consulting career."Depending on what he writes, it could be the end of a political consulting career or the rebirth of one," Smith said.But Shrum said his political consulting days are over, calling Sen. Jon Corzine, a Democrat who was elected governor of New Jersey last week, his final client. Now, Shrum said, he plans to focus on writing and teaching. He is a senior fellow at New York University Robert F. Wagner Graduate School of Public Service.The book is expected to hit the bookshelves in the spring of 2007.