WASHINGTON — Desperate presidents resort to desperate rhetoric, which calls new attention to their desperation. President Bush joined the club last week by citing U.S. failure in Vietnam to justify staying on in Iraq.

Bush’s comparison of the two conflicts rivals Richard Nixon’s “I am not a crook” utterance during Watergate and Bill Clinton’s “I did not have sexual relations with that woman, Miss Lewinsky,” in producing unintended consequences of a most damaging kind for a sitting president.

It is not just that Bush’s speech to the Veterans of Foreign Wars convention on Wednesday drew on a shaky grasp of history, spotlighted once again his own decision to sit out the Vietnam conflict, and played straight into his critics’ most emotive arguments against him and the Republican Party.

More importantly, Bush has called attention to the elephant that will be sitting in the room when his administration makes its politically vital report on Iraq to the nation next month. For Americans, the most important comparison will be this one: as Vietnam did, Iraq has become a failure even on its own terms — whatever those terms are at any given moment.

That is, the administration has constantly shifted its goals in Iraq to avoid accepting failure and blame — only to see the new goals drift beyond reach each time. Liberation of Iraqis became occupation by Americans, democracy became an unattainable centralized “national unity” government, and this year’s military surge has become a device for achieving political reconciliation among people who do not want to reconcile.

Bush’s appeal to Americans to turn away from “the allure of retreat” centered on the indisputably horrific consequences for the people of Vietnam and Cambodia of defeat in 1975. But his analogy also summons the historical reality that U.S. involvement in Indochina became untenable when that engagement itself became a threat to America’s own social fabric and national cohesion — and then to the very institutions that had responsibility for the war, the U.S. military and intelligence services, as well as the presidency and Congress.

Iraq fortunately has not produced anything like the scale of casualties and domestic conflict that Vietnam visited on the U.S. The two conflicts also differ greatly in their potential regional consequences. Bush had done well until now to steer away from such analogies.

But his words invite examination of the mounting damage that Bush’s approaches to the war in Iraq and to national security in general are doing to U.S. institutions in an American society that has significantly changed since 1975.

Some military commanders, CIA agents on the ground in Iraq, Republican members of Congress, State Department diplomats and others now make their highest priority the protection of their own reputations, careers and institutions — the three blend seamlessly into a single overriding ambition in Washington — for the post-Bush era, which thus draws closer, in the manner of a self-fulfilling prophecy.

The need to protect the White House, the Pentagon and both major political parties from greater Iraq fallout explains much of the blame being dumped on Iraqi Prime Minister Nouri al-Maliki at this late date — even though his deficiencies and close links to Iran and Syria were clearly visible when the administration helped install him in the job in 2006. As he has been throughout the Iraq experience, Bush is condemned to play the cards he dealt himself.

The prime minister’s chances of producing the “national unity” government that Bush demanded but that Maliki never seemed to believe in himself are now being shredded by the maneuvering for position in the twilight months of the Bush presidency.

The U.S. military is helping Sunni tribes organize into armed militias that will owe their loyalty beyond the tribe to American commanders rather than to Maliki’s government. Similarly the CIA has molded an Iraq intelligence service that draws no public funds from the Iraqi government and presumably is paid for by Langley. The agency’s reluctance to act against Kurdish rebels operating against Iran and Turkey may also be part of a separate vision of the agency’s future role in Iraq.

Such maneuvering is ultimately self-defeating, as was Bush’s desperate bid this week to mobilize on his side the old resentments and fears of the political battles fought over Vietnam. Bush’s speech fits Talleyrand’s definition of something worse than a crime: It was a blunder.

Vietnam and Iraq are totally different situations. But U.S. institutions and their leaders will still follow the Washington laws of self-preservation when campaigns abroad begin to threaten their survival.

Jim Hoagland is a Washington Post columnist. His e-mail address is jimhoagland@washpost.com.