Cambridge, Mass. ? Robert Caro, the biographer of Lyndon Johnson, delivered the annual Theodore H. White lecture last week at Harvard’s Joan Shorenstein Center on the Press, Politics and Public Policy, so it was inevitable that the panel following his talk was confronted with a question about the comparison between Johnson’s experience with Vietnam and President Bush’s travails in Iraq. (Editor’s note: Robert Caro is scheduled to speak at 8 p.m. today at the Lied Center of Kansas as part of the Dole Institute of Politics Presidential Lecture Series.)

Fortunately for the journalists who were sitting there, Ernest May, the distinguished professor of American history at Harvard, was called on to respond. May is a notably careful and hardheaded scholar, who over the years has been a frequent consultant to the National Security Council and the Department of Defense and is currently an adviser to the intelligence establishment.

Speaking on the morning after Bush’s news-conference defense of his policy in Iraq and the progress he claimed for that country, and on a day when the headlines told of fresh violence and additional casualties in Iraq, May did not mince words. The gap between official assessments of the situation and reports from the ground is “eerily reminiscent” of the Vietnam era. We know that the “credibility gap” in Vietnam was real, May said; what we don’t know at this moment is whether the “crumbling” in Iraq is as pervasive as it proved to be in Vietnam.

The mere fact that as dispassionate and non-hysterical an informed student of national security as Ernie May would not reject the Vietnam comparison out of hand speaks volumes. It adds to the impression left by Bush’s news conference that we have entered a new and politically risky stage of the Iraq conflict.

Watching Bush in his session with White House reporters, the single most striking impression was the president’s defensiveness. Barely two weeks ago, the White House set out to “correct” the negative cast it said the Washington press corps had placed on Iraq, with a series of upbeat statements from Bush, Vice President Cheney and other top officials.

That effort was cut short by the leak of a memo from Defense Secretary Donald Rumsfeld, questioning how much progress was really being made in the war on terrorism and describing the prospect in Iraq as “a long, hard slog.” The White House offensive was further overwhelmed by the news bulletins that produced the Tuesday headline in USA Today, “Violence in Iraq reaches new level.”

This is not the environment a president wants, as the calendar reminds him that his next date with the voters is just a year away. So Bush set out to influence public opinion by doing something he really does not like to do. For only the 10th time in his 33 months in office, he called a formal, full-scale news conference.

By my count, two-thirds of the questions dealt with aspects of the struggle in Iraq — and almost all of them started from a premise uncomfortable for the administration. There were reminders of the May 1 banner on the USS Abraham Lincoln — “Mission Accomplished,” a sign the president now disowns — and a citation of the casualties since then. There were questions about the costs of reconstructing Iraq and the lack of assistance from traditional allies, questions about the missing weapons of mass destruction and a blunt statement that “there are people out there who don’t believe that the administration is leveling with them about the difficulty and scope of the problem in Iraq.”

That last comment provoked an exasperated Bush to say, “I can’t put it any more plainly. Iraq’s a dangerous place.”

Administration loyalists may claim the questioning simply confirms Bush’s complaint about “negativism” in the Washington press corps. But I heard many of the same questions being raised by voters in Wisconsin when I was out there door-knocking the other week. And I believe Ernie May knows what he’s talking about.

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It was an odd coincidence that The New York Times, long resistant to the idea, announced the hiring of its first ombudsman — or “public editor,” as it prefers to call him — the same week that news came of the death of Charles Seib, who held the post of in-house critic and readers’ advocate at The Washington Post longer than anyone else. Seib, the longtime managing editor of the old Washington Star (and the man who gave me my first newspaper job in Washington), was a model of independence and sound news judgment throughout his worthy career. The Times is to be congratulated for finding Daniel Okrent, an experienced magazine editor, for its job. He seems to have the right credentials. And if he’s smart, he will look up some of Charley Seib’s ombudsman columns as a model he can hope to emulate.

David Broder is a columnist for Washington Post Writers Group.