"But he wouldn't do that." That sentiment is what made it possible for President Bush to stampede America into the Iraq war and to fend off hard questions about the reasons for that war until after the 2004 election. Many people just didn't want to believe that an American president would deliberately mislead the nation on matters of war and peace.

Now people with contacts in the administration and the military warn that Mr. Bush may be planning another war. The most alarming of the warnings come from Seymour Hersh, the veteran investigative journalist who broke the Abu Ghraib scandal. Writing in The New Yorker, Mr. Hersh suggests that administration officials believe that a bombing campaign could lead to desirable regime change in Iran - and that they refuse to rule out the use of tactical nuclear weapons.

"But he wouldn't do that," say people who think they're being sensible. Given what we now know about the origins of the Iraq war, however, discounting the possibility that Mr. Bush will start another ill-conceived and unnecessary war isn't sensible. It's wishful thinking.

As it happens, rumors of a new war coincide with the emergence of evidence that appears to confirm our worst suspicions about the war we're already in.

First, it's clearer than ever that Mr. Bush, who still claims that war with Iraq was a last resort, was actually spoiling for a fight. The New York Times has confirmed the authenticity of a British government memo reporting on a prewar discussion between Mr. Bush and Tony Blair. In that conversation, Mr. Bush told Mr. Blair that he was determined to invade Iraq even if U.N. inspectors came up empty-handed.

Second, it's becoming increasingly clear that Mr. Bush knew that the case he was presenting for war - a case that depended crucially on visions of mushroom clouds - rested on suspect evidence. For example, in the 2003 State of the Union address Mr. Bush cited Iraq's purchase of aluminum tubes as clear evidence that Saddam was trying to acquire a nuclear arsenal. Yet Murray Waas of the National Journal reports that Mr. Bush had been warned that many intelligence analysts disagreed with that assessment.

Was the difference between Mr. Bush's public portrayal of the Iraqi threat and the actual intelligence he saw large enough to validate claims that he deliberately misled the nation into war? Karl Rove apparently thought so. According to Mr. Waas, Mr. Rove "cautioned other White House aides in the summer of 2003 that Bush's 2004 re-election prospects would be severely damaged" if the contents of an October 2002 "President's Summary" containing dissents about the significance of the aluminum tubes became public.

Now there are rumors of plans to attack Iran. Most strategic analysts think that a bombing campaign would be a disastrous mistake. But that doesn't mean it won't happen: Mr. Bush ignored similar warnings, including those of his own father, about the risks involved in invading Iraq.

As Joseph Cirincione of the Carnegie Endowment for International Peace recently pointed out, the administration seems to be following exactly the same script on Iran that it used on Iraq: "The vice president of the United States gives a major speech focused on the threat from an oil-rich nation in the Middle East. The U.S. secretary of state tells Congress that the same nation is our most serious global challenge. The secretary of defense calls that nation the leading supporter of global terrorism. The president blames it for attacks on U.S. troops."

Why might Mr. Bush want another war? For one thing, Mr. Bush, whose presidency is increasingly defined by the quagmire in Iraq, may believe that he can redeem himself with a new Mission Accomplished moment.

And it's not just Mr. Bush's legacy that's at risk. Current polls suggest that the Democrats could take one or both houses of Congress this November, acquiring the ability to launch investigations backed by subpoena power. This could blow the lid off multiple Bush administration scandals. Political analysts openly suggest that an attack on Iran offers Mr. Bush a way to head off this danger, that an appropriately timed military strike could change the domestic political dynamics.

Does this sound far-fetched? It shouldn't. Given the combination of recklessness and dishonesty Mr. Bush displayed in launching the Iraq war, why should we assume that he wouldn't do it again?