Yesterday, Clarke poured fresh fuel on the political fire raging around the question of who should be blamed for the 11 September 2001 terrorist attacks, which killed 3,000 people.
"The reason I am strident in criticism of the president of the United States is because by invading Iraq -- something I was not asked about by the commission, it's something I chose to write about a lot in the book -- by invading Iraq, the president of the United States has greatly undermined the war on terrorism," Clarke said.
Clarke's testimony came a day after the commission released reports criticizing both the Clinton and Bush administrations for failing to aggressively pursue bin Laden. But his remarks have sparked an angry response from Republicans, and strike at the heart of Bush's re-election platform.
Bush is betting his presidential future on Americans' perception of him as a successful "war president." But his rival, Democratic Senator John Kerry, argues that Bush policy decisions like the Iraq war have not made the world a safer place.
Clarke's comments on Iraq yesterday drew a sharp rebuke from Republican panel member John Lehman. The former Navy secretary told Clarke he may have a credibility problem as his comments strongly favor Kerry and appear aimed at selling his book.
Clarke responded by saying he registered as a Republican in the 2000 elections -- an indication he voted for Bush. He also said he would not accept any position in a Kerry administration.
Clarke also blamed himself for not doing enough to stop 9/11. Drawing applause from the hearing-room audience -- which included family members of the 11 September victims -- Clarke apologized for his role and the role of the government in failing to prevent the attack.
"To them who are here in the room, to those who are watching on television: Your government failed you. Those entrusted with protecting you failed you. And I failed you. We tried hard, but that doesn't matter, because we failed. And for that failure, I would ask, once all the facts are out, for your understanding and for your forgiveness," Clarke said.
But as in his book, he clearly drew a line between the way he says the Clinton and Bush teams tackled terrorism.
"My impression was that fighting terrorism in general, and fighting Al-Qaeda in particular, were an extraordinarily high priority in the Clinton administration. Certainly [there was] no higher priority," Clarke said.
As for the Bush White House, Clarke said, "I believe the Bush administration in its first eight months considered terrorism an important issue, but not an urgent issue."
In his testimony yesterday, Clarke said that on 4 September 2001 -- one week before the 11 September attacks -- he wrote a letter to National Security Adviser Condoleezza Rice, urging her to step up counterterrorism efforts and asking her to imagine how she and others would feel if an attack killed hundreds of Americans.
Rice has declined to give public testimony to the 11 September commission. Deputy Secretary of State Richard Armitage yesterday testified in her stead.
Clarke's book contends that as early as 12 September, the Bush administration, rather than focusing on Al-Qaeda, was looking for ways to tie the attacks to Iraq and Saddam Hussein. That claim was disputed by an array of Bush officials this week, including Defense Secretary Donald Rumsfeld.
Rumsfeld told the panel that the administration had spent months devising a plan against Al-Qaeda that was completed just before 9/11.
But panel co-chair Bob Kerrey, a former Democratic senator, said yesterday that he had seen the still-secret plan and was not impressed:
"We heard both [Deputy Defense] Secretary [Paul] Wolfowitz and [Defense] Secretary [Donald] Rumsfeld refer to the failure of the Clinton administration to deliver a plan dealing with Al-Qaeda, and they spent seven or eight months developing their own plan. I was briefed this morning on that plan, and I would say fortunately for the administration it's classified, because there's almost nothing in it. It calls for more diplomacy; it calls for increased pressure, basically the same thing that [CIA] Director Tenet just talked about, using tribal [fighters] against Al-Qaeda; and lastly calls for some vague things to try to oust [Taliban leader] Mullah Omar," Kerrey said.
Still, both Rumsfeld and his predecessor under Clinton, William Cohen, testified yesterday that they did not believe killing bin Laden would necessarily have prevented the attacks.
CIA Director George Tenet agreed with that. But testifying yesterday, Tenet admitted that more could have been done to foil the attacks, even as he dismissed criticism that the agency acted too cautiously.
"We didn't steal the secret that told us what the plot was. We didn't recruit the right people or technically collect the data, notwithstanding enormous effort to do so. We didn't integrate all the data we had properly, and probably we had a lot of data that we didn't know about that, if everybody had known about, maybe we would have had a chance. I can't predict to you one way or another," Tenet said.
The commission of five Republicans and five Democrats, most of them former legislators or senior officials, is due to issue its final report in late July at the height of the presidential campaign. Its findings are likely to have an impact on Bush's re-election prospects.
The testimony to date has revealed that an abundance of intelligence in the summer of 2001 indicated a major attack was in the making. Yet according to Clarke, the former counterterrorism boss could not get the incoming Bush administration to convene a top-level meeting to discuss the Al-Qaeda threat.
Commissioner Jamie Gorelick, a deputy attorney general under President Bill Clinton, said the intelligence briefings given to Bush before 11 September about the gathering threats "would set your hair on fire."