The president of the United States in the last debate chose to go on the attack against his challenger, Mitt Romney – and once again largely failed to convince the American people that he was the more presidential alternative.

But how did the once-messianic incumbent find himself in this fix of playing the catch-up role of a bar-room-brawling challenger rather than a calm and confident president? Despite running ahead in the polls for most of the year, Barack Obama has rarely achieved a 50 percent favorability rating, largely because of four years of dismal economic news. Obama himself had warned us four years ago that if he didn’t restore prosperity, he would be a one-term president – and the debates taught us that he was probably right.

Promises about halving the annual deficit, getting unemployment below 6 percent and increasing middle-class incomes were never met. The recent unrest in the Middle East and the killing of an American ambassador and three other Americans in Libya did not help convince anyone that Obama’s foreign policy was so successful that they could afford to overlook an anemic economy.

Yet the American people always wanted a viable alternative before they admitted their mistake and dumped a president whom they had voted in with such adulation in 2008. Obama sensed that hesitancy, and so he spent nearly $1 billion in a largely negative campaign to convince voters that Romney was insensitive to women, callous to the poor and, in general, a heartless, out-of-touch capitalist. The implicit message was that even if Obama’s first term had not worked out as promised, Romney would nevertheless be even worse. The lesser of two evils, not a successful four years, had replaced hope and change this time around.

But after three debates, voters at last got to know Romney. What they saw and heard was quite different from the villain of the attack ads. In the first encounter, even the pro-Obama media came away shocked that the supposedly aristocratic Romney proved more personable – and more knowledgeable – than the listless Obama. The president showed up as if the entire debate were a tedious chore – as if Romney could not possibly win the debate, and even if he did, it would have no effect on the media or on Obama’s steady lead in the polls.

Instead, Obama’s terrible 90 minutes set off a chain reaction, eroding the president’s lead in the critical swing states. In the fireworks of the second debate, with its town-hall format, Obama came out fiery and accusatory, and pulled off a tie or narrow victory based on his sheer aggression – or on the fact that he at least had improved upon his first losing debate performance.

The trick for Obama in the second outing was to show Americans that the first debate had been a freakish anomaly – and Romney really was the caricature that had been depicted during months of negative ads. Yet if Obama won tactically, he lost strategically through his combative demeanor and the very fact that Romney was not only still standing after three cumulative hours of head-to-head jousting, but gaining even more ground in the polls.

This week, the third and final debate offered Obama a last opportunity to convince the American people that at least on matters of foreign policy, Romney was either dangerous or ill-informed. That challenge also ensured that Obama would have to crowd into the final 90 minutes near-constant attacks to crack the calm Romney facade. Even or ahead in the polls, all Romney had to do in response was for a third time keep acting presidential and prove that his earlier displays of composure and competence were no flukes – a no-brainer strategy clear to anyone who had followed the first two debates.

That is precisely what Romney pulled off. As in the second debate, Obama might have done well enough to come away with a tie or even a narrow win on points, but he probably didn’t fare well enough to reverse his slide in the polls. If Obama sought to shatter Romney’s image as a compassionate and competent captain of industry, he more likely damaged his own once carefully crafted image as a nice guy.

So what did we learn from nearly five hours of verbal gymnastics?

The image of competency and composure that Romney projected in the first debate was not altered by the second and has been confirmed by the third. Presidential debates really do matter, and a few hours of engagement with Romney may have cost Obama what he had tried to ensure through six months of attack-dog campaigning. And so in the last 10 days of the campaign, Obama will have to return to negative advertising – a last hope to achieve through personal attacks what he couldn’t accomplish through public persuasion.

If voters conclude that Obama is desperate to demonize Romney in a way he could not in the fair match of the public debates, then Obama will probably lose the election.

© 2012 TRIBUNE MEDIA SERVICES, INC.