Speaking on ABC's "Good Morning America" today, McClellan's predecessor and former boss Ari Fleischer said his one-time deputy left the White House "on a bad note and had a difficult tenure while he was there. … I think he's taking that out on the president. He's inventing facts after he left to say the president manipulated information."
"This is heartbreaking to me," said Fleischer. "Anybody can do this and turn 180 degrees. It makes me wonder did Scott believe the things he said from the podium?"
Fleischer said McClellan was only the assistant press secretary during the lead up to the Iraq War and was out of the loop when it came to many of the major policy decisions.
"He wouldn't have been in those loops, nobody is for those type of meetings. [But] that's what the he wrote the book about," he said.
On Wednesday, current White House press secretary Dana Perino characterized the book as a sad rant by a "disgruntled" employee.
McClellan told NBC that he not surprised by the response.
"I expected these kind of attacks," he said, "but there is a larger purpose here."
Much of the book focuses on the administration's rationale for going to war in Iraq. He criticizes Secretary of State Condoleezza Rice, who served as the national security adviser in the lead up to the war, for worrying too much about protecting her reputation.
Rice, he told NBC, was "too accommodating of the president's views instead of questioning and challenging them."
He said that she was "too deferential to those individuals," meaning Vice President Dick Cheney and former Secretary of Defense Donald Rumsfeld.
Rice would not comment specifically to McClellan's accusations, but told The Associated Press that the president was honest about the reasons for the war.
"I am not going to comment on a book that I haven't read," she told the AP, "but what I will say is that the concern about weapons of mass destruction in Saddam Hussein's Iraq was the fundamental reason."
ABC News' Jennifer Parker contributed to this report.