The open secret of Washington memoirs is that they typically confirm what we already know or suspect. In the case of the excerpts from the forthcoming book by Robert Gates, who was Defense Secretary for two years under George W. Bush and two and a half under President Obama, this isn't reassuring.

Mr. Gates's revelations include that Mr. Obama and Hillary Rodham Clinton admitted that their opposition to the 2007 Iraq surge of troops was entirely political; that Vice President Joe Biden is a blowhard who "has been wrong on nearly every major foreign policy and national security issue over the past four decades"; that Mr. Obama didn't believe in his own Afghanistan strategy and wanted mainly to get out from the first day; that the White House national security staff is full of political operatives who like to push generals around, and that Congress is mostly a crowd of parochial-minded bullies.

None of this is news—at least not to anyone who has been paying reasonable attention. Mr. Gates's contribution is to provide confirming detail and judgment from a source the media consider credible, and in that sense his memoir is educational and disconcerting.

That's especially so on matters of war, when American lives are on the line. Whatever one thinks of the 2003 decision to go to war in Iraq, Mr. Bush's 2007 troop surge and strategy shift were gutsy calls and an historic success. They defeated al Qaeda in Iraq and created space for a long-term U.S.-Iraqi partnership that Mr. Obama later abandoned by refusing to leave some troops behind a la South Korea or Japan.

Readers may recall that at the height of the surge in September 2007, General David Petraeus reported to the Senate on its early but still uncertain progress. Then Senators Obama and Clinton were withering in their attacks on the surge and its chances for success.

After the duo had ascended to the executive branch, Mr. Gates writes that in one meeting "Hillary told the president [Obama] that her opposition to the [2007] surge in Iraq had been political because she was facing him in the Iowa primary. . . . The president conceded vaguely that opposition to the Iraq surge had been political. To hear the two of them making these admissions, and in front of me, was as surprising as it was dismaying."

Mr. Obama won the Presidency despite his dreadful surge judgment, but his habit of treating war mainly as domestic politics has carried over to the Oval Office and undermined his own policies. That's especially true in Afghanistan, as Mr. Gates reports that by early 2010 he had concluded that the President "doesn't believe in his own strategy, and doesn't consider the war to be his. For him, it's all about getting out."

This was only weeks after Mr. Obama had ordered a troop surge in which thousands of Americans gave their lives. Mr. Gates's revelations explain why Mr. Obama has so rarely spoken about the Afghan mission to the American people, why he undermined it with an exit date before it even began, and why the Taliban and Pakistan have figured they can wait us out.

As for Mrs. Clinton, she's supposed to be made of sterner stuff. But her cynical surge opposition, despite counsel from such Petraeus intimates as former General Jack Keane, should be a mark against her as a potential President. Mr. Obama lacked any convictions on war, but Mrs. Clinton lacked the courage of hers.

The Gates book may be most troubling for what it says about the three long years left in Mr. Obama's second term—which also makes us wonder why he didn't go public sooner, at the time he left office. He describes a President who knows he must invoke the traditional rhetorical markers of U.S. foreign policy—a strong defense, credibility with allies, democracy and human rights—yet whose every impulse is to leave the world to its own devices. That's especially dangerous when the American public is in an inward-looking mood. The U.S. needs a President willing to make the case for continued American engagement and leadership.

Mr. Gates's account also helps to explain why America's friends are worried (Israel) or increasingly going their own way (the Saudis), while our enemies (Iran, al Qaeda) are confident that now is a time to advance. They didn't need a memoir to draw those conclusions, but they too have taken the measure of Mr. Obama and the lack of will behind his words.

With such a President, it is going to be up to some of Congress's few grown-ups to steer the country away from the dangers ahead and avoid lasting damage to U.S. security and world order. Any candidates?