He's obviously a big source for it, but couldn't be as outspoken as now b/c he was still in the administration. It's a bit long, though, but good reading. I'm not sure it will sway true believers, but it is the original story and does point out that he was saying similar things a year and a half ago.
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http://www.time.com/time/nation/article/0,8599,333835,00.html)
But for his more forceful statements, any number of articles from the last couple of days detailing his current statements made in conjunction with the release of his book would suffice for the points you mention. Just search Google News for "Richard Clarke".
Also, he isn't the only one to make these claims. Point to former Treasury Secretary's claims that the Bush administration was obsessed with Iraq from Day One. But the thing is, everyone knew this anyway! Wolfowitz wrote about it proudly, Rumsfeld clamored for a link to Iraq immediately after 9-11, and the whole gang wrote (Cheney, Wolfowitz, Rumsfeld, Libby, Jeb Bush... under the name PNAC) that their policy included overthrowing Iraq with or without provocation. In a formal letter to the WH, they urged that Clinton do this, but he didn't bite.
Clarke said on Charlie Rose last night that he doesn't understand why they bother to just come out and SAY they were obsessed with Iraq, b/c it is completely obvious and a known fact. "Why deny the obvious?", I think he said.