Scott McClellan’s admission that he unintentionally made false statements denying the involvement of Karl Rove and Scooter Libby in the Bush-Cheney administration’s plot to discredit former Ambassador Joe Wilson, along with his revelation that Vice President Dick Cheney and President Bush were among those who provided him with the misinformation, sets up the former White House press secretary as John Dean to George Bush’s Richard Nixon.

It was Dean’s willingness to reveal details of what he described as “a cancer” on the Nixon presidency that served as a critical turning point in the struggle by a previous Congress to hold the 37th president to account.

Now, McClellan has offered what any honest observer must recognize as the stuff of a similarly significant breakthrough.

But is the current Congress up to the task of holding the 43rd president to account?

What McClellan has revealed is a stunning indictment of the president and vice president. The former press secretary is confirming that Bush and Cheney not only knew that Rove, the administration’s political czar, and Libby, who served as Cheney’s top aide, were involved in the scheme to attack Wilson’s credibility – by outing the former ambassador’s wife, Valerie Plame, as a Central Intelligence Agency analyst – but that the president and vice president actively engaged in efforts to prevent the truth from coming out.

“The most powerful leader in the world had called upon me to speak on his behalf and help restore credibility he lost amid the failure to find weapons of mass destruction in Iraq. So I stood at the White house briefing room podium in front of the glare of the klieg lights for the better part of two weeks and publicly exonerated two of the senior-most aides in the White House: Karl Rove and Scooter Libby,” writes McClellan in an excerpt from his book, What Happened, to be published in April by Public Affairs.

“There was one problem,” he continues. “It was not true. I had unknowingly passed along false information. And five of the highest-ranking officials in the administration “were involved in my doing so: Rove, Libby, the vice president, the president’s chief of staff, and the president himself.”

Much has been made about the fact that outing Plame as a CIA operative was a felony, since knowingly revealing the identity of an intelligence asset is illegal. And much will be made about the fact that McClellan’s statement links Bush and Cheney to the cover-up of illegal activities and the obstruction of justice, also felonies.

But a bigger issue is at stake. If the president and vice president knowingly participated in a scheme to attack a critic of their administration – Wilson had revealed that the White House had been informed that arguments Bush and Cheney used for attacking Iraq were ungrounded – they have committed a distinct sort of offense that the House Judiciary Committee already has determined as grounds for impeachment.

In the summer of 1974, Democrats and Republicans on the committee voted overwhelmingly to recommend the impeachment of President Richard Nixon for having “repeatedly engaged in conduct violating the constitutional rights of citizens, impairing the due and proper administration of justice and the conduct of lawful inquiries, or contravening the laws governing agencies of the executive branch and the purposes of these agencies.”

That second article of impeachment against Nixon detailed his involvement in schemes to use the power of his position to attack political critics and then to cover up for those attacks.

McClellan’s statement demands the sort of inquiry and action that Dean’s statements regarding Nixon demanded three decades ago.

As former Common Cause president Chellie Pingree notes, “The president promised, way back in 2003, that anyone in his administration who took part in the leak of Plame’s name would be fired. He neglected to mention that, according to McClellan, he was one of those people. He fired no one, stonewalled the press and the federal prosecutor in charge of the case, and lied through his teeth.”

Pingree, who is bidding for an open House seat representing her native Maine, argues that the Judiciary Committee must subpoena McClellan as part of a renewed investigation of the Wilson case.

She is right.

She is right, as well, when she concludes that, if what McClellan says is true, “it will call into question the legitimacy of the entire administration. And we may see a changing of the guard at the White House sooner than expected.”

That changing of the guard – via the constitutional process of impeachment and trial for their various and sundry high crimes and misdemeanors – is overdue.

JOHN NICHOLS IS WASHINGTON CORRESPONDENT FOR THE NATION MAGAZINE.