Who is Rand Beers?
The question is important, in this context of Clarke push-back: Beers and Clarke are old friends, and Beers is John Kerry's chief foreign policy advisor. Hance, pushback evidence # 2: Clarke is further shown to be publishing this book as a campaign favor to Kerry.
Not likely. Here's TPM:

[Beers is] a career government national security expert specializing in intelligence and counter-terrorism. He's a registered Democrat. But his profile is that of an apolitical civil servant -- enough so that he was asked to work for Reagan, Bush, Clinton and the current President Bush in various capacities.

In August 2002 Condi Rice hired him to be the special assistant to the president for combating terrorism at the NSC. In a sense that was the job that Clarke had before 9/11, although by that point the chairs had been shuffled around so much that no direct comparison is really possible.

In any case, he came in in August 2002 and he resigned about seven months later, a few days before the beginning of the war. Eight weeks after that he signed up to work for John Kerry.

Marshall also cites this Post write up on Beers, from last summer.

No single issue has defined the Bush presidency more than fighting terrorism. And no issue has both animated and intimidated Democrats. Into this tricky intersection of terrorism, policy and politics steps Beers, a lifelong bureaucrat, unassuming and tight-lipped until now. He is an unlikely insurgent. He served on the NSC under Presidents Ronald Reagan, George H.W. Bush, Bill Clinton and the current Bush. The oath of office hangs on the wall by his bed; he tears up when he watches "The West Wing." Yet Beers decided that he wanted out, and he is offering a rare glimpse in.