MUCH OF THE debate in this presidential campaign has been rhetoric about rhetoric: accusations that the other side has somehow strayed beyond the bounds of fair play. These tend to be fairly one-sided conversations. Democrats can call President Bush a liar, accuse Vice President Cheney of corruption and hint that the administration is secretly hiding Osama bin Laden to be produced in an October surprise, and still maintain with a straight face that they may lose because they don't know how to be as vicious as Karl Rove. Republicans can label Sen. John F. Kerry a treasonous flip-flopper and insist piously that they (unlike the Democrats) are only debating the issues.

To a certain extent, there's nothing new in this: Candidates have been going negative while decrying negativity for about as long as there have been campaigns. But two types of accusations seem particular to this year and to the dilemmas of waging politics in wartime. The first concern Republican suggestions that Mr. Kerry's policies would leave the United States vulnerable to a terrorist attack; the second, Republican accusations that Mr. Kerry is emboldening the enemy and undermining U.S. troops when he criticizes Mr. Bush's policy in Iraq.

The Kerry team says both lines of criticism hit below the belt, but in the first instance we're not all that sympathetic. Yes, the debate ought to proceed with the presumption that both candidates are patriots who want to keep America safe; and yes, anyone claiming to know whom the terrorists favor just makes himself look silly. But Mr. Cheney's remarks about the Kerry terrorism policy, while pretty rough, pertain to questions that are central to this campaign: What is the right way to fight the war on terrorism? Who is the enemy? Which president could keep the country safer? Mr. Kerry is arguing that the nation is less safe because Mr. Bush waged war in Iraq and paid too little attention to al Qaeda; that's a legitimate case to present to voters. Mr. Cheney is arguing that Mr. Kerry's voting history on the use of force and his shifting statements on Iraq foreshadow a leader who would not meet the terrorist threat vigorously enough, and he's entitled to make that argument.

The attacks on Mr. Kerry's criticisms of Iraq policy, by contrast, are inexcusable. It's true that the insurgents in Iraq are fighting a war for public opinion here and in allied countries; they kidnap and murder in an effort to sap America's will to fight the war. But the response to that can't be to stifle debate in this country. We think Mr. Kerry and his campaign are ill-advised to belittle the contributions of Polish and British allies, or to label Iraqi Prime Minister Ayad Allawi a puppet. But he's entitled to state that case, too. A leader can maintain public support for a difficult war only by, first, formulating a policy that Americans will believe has some chance of success and, second, credibly describing that policy, along with its challenges and setbacks. Mr. Bush's deficiencies in those regards can't be overcome by lashing out at his critics.