Manning was turned in late last month by a former computer hacker with whom he spoke online. In the course of their chats, Manning took credit for leaking a headline-making video of a helicopter attack that Wikileaks posted online in April. The video showed a deadly 2007 U.S. helicopter air strike in Baghdad that claimed the lives of several innocent civilians.

He said he also leaked three other items to Wikileaks: a separate video showing the notorious 2009 Garani air strike in Afghanistan that Wikileaks has previously acknowledged is in its possession; a classified Army document evaluating Wikileaks as a security threat, which the site posted in March; and a previously unreported breach consisting of 260,000 classified U.S. diplomatic cables that Manning described as exposing "almost criminal political back dealings."

His favorite stuff, allegedly, was the diplomatic stuff:

That seemed to be the least interesting information to Manning, however. What seemed to excite him most in his chats was his supposed leaking of the embassy cables. He anticipated returning to the states after his early discharge, and watching from the sidelines as his action bared the secret history of U.S. diplomacy around the world.

"Everywhere there's a U.S. post, there's a diplomatic scandal that will be revealed," Manning wrote. "It's open diplomacy. World-wide anarchy in CSV format. It's Climategate with a global scope, and breathtaking depth. It's beautiful, and horrifying."

And as for his security clearance:

Manning told Lamo that he enlisted in the Army in 2007 and held a Top Secret/SCI clearance, details confirmed by his friends and family members.

SNIP

Manning had access to two classified networks from two separate secured laptops: SIPRNET, the Secret-level network used by the Department of Defense and the State Department, and the Joint Worldwide Intelligence Communications System which serves both agencies at the Top Secret/SCI level.

From the Wikipedia, not for use for academic research or very small children:

At a July 5, 2001 White House gathering of the FAA, the Coast Guard, the FBI, Secret Service and INS, Clarke stated that "Something really spectacular is going to happen here, and it's going to happen soon." Donald Kerrick, a three-star general who was a deputy National Security Advisor in the late Clinton administration and stayed on into the Bush administration, wrote Hadley a classified two-page memo stating that the NSA needed to "pay attention to Al-Qaida and counterterrorism" and that the U.S. would be "struck again." As a result of writing that memo, he was not invited to any more meetings.

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Many of the events Clarke recounted during the hearings were also published in his memoir. Among his highly critical statements regarding the Bush Administration, Clarke charged that before and during the 9/11 crisis, many in the administration were distracted from efforts against Osama bin Laden's Al-Qaeda organization by a pre-occupation with Iraq and Saddam Hussein. Clarke had written that on September 12, 2001, President Bush pulled him and a couple of aides aside and "testily" asked him to try to find evidence that Saddam was connected to the terrorist attacks. In response he wrote a report stating there was no evidence of Iraqi involvement and got it signed by all relevant agencies, including the Federal Bureau of Investigation and the CIA. The paper was quickly returned by a deputy with a note saying "Please update and resubmit".[11] After initially denying that such a meeting between the President and Clarke took place, the White House later reversed its denial when others present backed Clarke's version of the events.[12][13]

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Want more details?  From www.historycommons(dot)org:

Donald Kerrick. [Source: White House]Clinton and Bush staff overlap for several months while new Bush appointees are appointed and confirmed. Clinton holdovers seem more concerned about al-Qaeda than the new Bush staffers. For instance, according to a colleague, Sandy Berger, Clinton's National Security Adviser, had become "totally preoccupied" with fears of a domestic terror attack. [Newsweek, 5/27/2002] Brian Sheridan, Clinton's outgoing Deputy Defense Secretary for Special Operations and Low-Intensity Conflict, is astonished when his offers during the transition to bring the new military leadership up to speed on terrorism are brushed aside. "I offered to brief anyone, any time on any topic. Never took it up." [Los Angeles Times, 3/30/2004] Army Lieutenant General Donald Kerrick, Deputy National Security Adviser and manager of Clinton's NSC (National Security Council) staff, still remains at the NSC nearly four months after Bush takes office. He later notes that while Clinton's advisers met "nearly weekly" on terrorism by the end of his term, he does not detect the same kind of focus with the new Bush advisers: "That's not being derogatory. It's just a fact. I didn't detect any activity but what [Clinton holdover Richard] Clarke and the CSG [Counterterrorism Security Group] were doing." [Washington Post, 1/20/2002] Kerrick submits a memo to the new people at the NSC, warning, "We are going to be struck again." He says, "They never responded. It was not high on their priority list. I was never invited to one meeting. They never asked me to do anything. They were not focusing. They didn't see terrorism as the big megaissue that the Clinton administration saw it as." Kerrick adds, "They were gambling nothing would happen." [Los Angeles Times, 3/30/2004] Bush's first Joint Chiefs of Staff Chairman, Henry Shelton, later says terrorism was relegated "to the back burner" until 9/11.

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