“I’m the first one to confess that the spirit that I brought to Washington, that I wanted to see instituted, where we weren’t constantly in a political slugfest … I haven’t fully accomplished that. Haven’t even come close in some cases…. My biggest disappointment is that we haven’t changed the tone in Washington as much as I would have liked.” –President Barack Obama on “60 Minutes,” Sunday, Sept. 23

It was the commitment at the core of Barack Obama’s candidacy, the most important promise he made to the American people: He would unify a divided nation. Again and again, he vowed to repair the political breach. To end the bitter polarization of American life, to do away with “slash-and-burn” politics that “tear us apart instead of bringing us together” – above all else, that was the hope and the change he offered.

At every milestone in Obama’s journey to the White House – from the keynote address in Boston that put him on the national radar screen to his inaugural address in 2009 – he held himself out as a healer. Skeptics might note that partisanship and rancor were as old as American democracy itself, but Obama insisted that would change when he was president. The toxic style of politics wasn’t inescapable. Give me the highest office in the land, he assured a rapturous crowd in Ohio two days before the 2008 election, and “we can end it once and for all.”

Millions of voters believed him. They took to heart his vow to transfigure American public life. They looked forward to the uplifting leadership he promised. What they got instead was the most polarizing and divisive presidency in modern times. The civility and goodwill that were to be Obama’s touchstone? “I haven’t fully accomplished that,” he concedes. “Haven’t even come close.”

As the 2012 campaign heads into the home stretch, a story in Politico notes that “Obama and his top campaign aides have engaged far more frequently in character attacks and personal insults than the Romney campaign.” The man who won the presidency by decrying “partisanship and pettiness and immaturity” now seeks reelection by deploying slurs and aspersions with abandon: A key aide suggests that Mitt Romney’s financial filings may amount to a felony. The vice president claims that Republicans want to put voters “back in chains.” An Obama campaign video likens Romney to “a vampire.”

“The Obama-led attacks on Romney’s character,” Politico concludes, “have been both relentless and remorseless.”

Of course there is nothing new about ruthlessness in politics. For all of Obama’s talk about not wanting “to pit red America against blue America,” it was always foreseeable that his reelection campaign would eventually become a merciless march to the sea.

Yet Obama’s brutal negativity can’t simply be brushed aside as the inevitable surrender of idealism to realism. It’s true that presidents have often lamented the shrillness of American politics. Abraham Lincoln sought to “bind up the nation’s wounds.” George W. Bush originally ran for office as “a uniter, not a divider.” Even Richard Nixon said his “great objective” would be “to bring the American people together.” But only Obama made national unity and bipartisan harmony the justification for his candidacy.

It never happened. The 44th president has been nothing like the healer-in-chief he promised to be. Early on he took the low road, inflaming resentments, demonizing his critics, and, yes, pitting red Americans against blue Americans. His defenders argue that he had no choice – that in the face of unremitting Republican opposition, going negative was his only option.

But all presidents face partisan opposition. Democrats vehemently fought Bush; Republicans fiercely battled Bill Clinton. Obama never conditioned “hope and change” on GOP support for his agenda. His condition was that he be elected.

“2008’s candidate of hope stands poised to become 2012’s candidate of fear,” New York Magazine’s John Heilemann wrote last spring. “For anyone still starry-eyed about Obama, the months ahead will provide a bracing revelation about what he truly is: not a savior, not a saint, not a man above the fray, but a brass-knuckled, pipe-hitting, red-in-tooth-and-claw brawler determined to do what is necessary to stay in power.”

The president says now that his “biggest disappointment” is that he hasn’t been able to elevate the tone of American politics. For countless voters, a far bigger disappointment may be that he never tried.

(Jeff Jacoby is a columnist for The Boston Globe. His website is www.JeffJacoby.com).