On the eve of the first critical presidential debate of 2012, why is the campaign of Mitt Romney suddenly showing signs of imploding?

There has been no marked improvement in the dim economic picture, to which he has pinned his hopes of ousting President Obama. Indeed, the slow national growth rate has reportedly slipped slightly again. Yet opinion polls in state after state indicate leakage in support for Mr. Romney, notably in swing states like Ohio and Florida.

Certainly, the disclosure of his remarks at that closed fund-raiser in Florida — in which he wrote off the "47 percent of Americans" who don't pay federal income taxes — was a contributor. His appraisal revealed a narrow and almost contemptuous view of voters beyond his grasp, and underscored his focus on only those who would vote for him.

The fact that Mr. Romney spoke in the apparent belief that he was being heard only by like-minded big contributors gave damaging credibility to his candor. And his hapless effort to recover by saying publicly that he intended, if elected, to be president of "100 percent of Americans" failed to convince.

Yet Mr. Romney's slide appeared actually to have begun after the two national party conventions, and particularly after the Democratic event in Charlotte, which proved to be better organized and more entertaining. The quartet of chief speakers — Barack and Michelle Obama, Vice President Joe Biden and, most of all, former President Bill Clinton — seemed to ignite some of the old Democratic passion that had been so evident four years earlier.

Mr. Clinton especially plugged old Democratic heartstrings and memories by taking head-on the question that the Republicans had so hopefully raised at their convention in Tampa — the old Ronald Reagan inquiry, "Are you better off than you were four years ago?" Mr. Clinton made a strong case for the affirmative by reminding the audience of the America he had left to George W. Bush in 2001, and what Mr. Obama had done in four years to clean up the mess Bush created.

This display of Democratic political firepower was in contrast to the man-who-wasn't-there at the earlier Republican pow-wow, who had left as part of his legacy two unfinished wars and America's reputation abroad in shreds. Many Democratic voters and others appeared to come away from the Charlotte convention thinking that, although they were not in great shape yet, they were better off after all than they were four years earlier.

At the same time, Mitt Romney was saying or doing nothing much to convince many voters that, even with his business record as Mr. Fix-it, he had the answers to right the economy. His insistence on riding a vague five-point plan for recovery instead of opening his magic box of specific cures was puzzling, despite repeated urging from the press. He was proving not to be the salesman his father was, who sold America on cheaper, smaller cars at American Motors in the late 1960s.

So now Mitt Romney finds himself only few days away from a do-or-die national television debate with President Obama, needing not merely to demonstrate he can hold his own with the President of the United States but to jolt his campaign back to life with a dazzling performance.

Some Democrats have tried to set Mr. Romney up by contending he has the edge entering the first of the three presidential face-offs. After all, they argue, he successfully ran the gauntlet of numerous primary debates last winter and spring. That is nonsense. Mr. Obama clearly demonstrated his own debating skills four years ago, first against Hillary Clinton and then against John McCain. Mr. Romney will have his hands full just holding his own.

A mini-debate has been going on over whether these debates are as decisive as proponents contend. This time around, however, given the politically wounded state in which Mr. Romney will enter the fray Wednesday night, there is little doubt a solid and impressive showing will be critical to keeping his candidacy afloat in the campaign's final month.

Jules Witcover is a syndicated columnist and former long-time writer for The Baltimore Sun. His latest book is "Joe Biden: A Life of Trial and Redemption" (William Morrow). His email is juleswitcover@comcast.net.