As he climbed the political heap, a young Barack Obama roused audiences with promises to unite the nation. He was a Senate candidate in 2004 when he told the Democratic national convention, “There is not a liberal America and a conservative America. There is a United States of America.”

In 2007, he declared early in his presidential run that “I don’t want to pit red America against blue America. I want to be the president of the United States of America.”

A year later, after he won the Iowa caucus, he promised, “We are not a collection of red states and blue states. We are the United States of America.”

And on the November night in 2008 when he was elected president, he insisted his victory proved “we have never been just a collection of individuals or a collection of red states and blue states. We are, and always will be, the United States of America.”

Oh, well, that was then. Reading those “yes we can” speeches now is like gawking at museum relics. Obama’s promise to heal a polarized nation has proven to be as big a lie as his promise that you can keep your health insurance.

America is now so divided and demoralized that there is no hope Obama can fix it. As last week proved, he doesn’t even pretend to try any more.

On the same day that he supported his party’s move to neuter Republican power in the Senate by restricting the filibuster, 37 news organizations complained that the White House was acting like the ­Soviet Union in manipulating public opinion.

Journalists argued that Obama aides block news photographers from official events, then use government workers to take pictures and videos of him for social-media sites.

“This is just like Tass,” a New York Times photographer told his paper, referring to the Soviet propaganda arm. “It’s like government-controlled use of the public image of the president.”

Meanwhile, Obama met with a gaggle of far-left pundits to drum up support as he battles record-low polls.

The developments are snapshots in the collapse of a presidency.

More and more people are realizing that Obama’s idea of unity is that everybody must agree with him, and that he has no tolerance for those who don’t. Yet he ­responds to this awakening by ­digging himself deeper into a partisan hole. Step away from the shovel, Mr. President.

Historians, I believe, will conclude that his refusal to roll up his sleeves and honestly engage critics was a character flaw that morphed into a political strategy. Despite the flowery promises to unite the country, or maybe because of them, he boxed himself into a pose of being above politics. His aggrandizing self-regard and contempt for others leaves him incapable of routine compromise.

Confronted with problems, he ­defaults to one of two options: total domination or total surrender. The result is that he is a Caesar wannabe at home and a Chamberlain abroad. As he stiff-arms Republicans and most of the media, he seems ready to accept a nuclear-armed Iran.

Even as his support falls below 40 percent and a majority say they don’t trust him, he paints himself as the victim.

He defended his party’s decision to end the long Senate tradition of requiring 60 votes for most appointments by saying Republicans are determined to “obstruct everything . . . Just to refight the results of an election.”

See, it’s all about him. Never mind that other presidents struggled with the same rules. Never mind that opponents, including some Democrats, have legitimate differences with him and want him to work harder to build a consensus for the good of the country.

And never mind his obvious ­hypocrisy on changing the rules. In his first year in the Senate, with the GOP holding the majority, he warned that one-party rule would mean “the bitterness and the gridlock will only get worse.”

That Barack Obama was a man to admire. He made history by promising to restore Americans’ trust in each other and their government.

“I will always be honest with you about the challenges we face. I will listen to you, especially when we disagree,” he vowed on election night in 2008.

Five years later, Americans finally are being honest with themselves.

They now realize that Barack Obama doesn’t exist anymore, if he ever did.

Hill of beans

Noting that Hillary Clinton received yet another award the other day, a friend writes: “Her life has become one long victory lap, but I’m trying to figure out what victory she actually won.”

Shrunken ‘Empire’

The 50th anniversary of the JFK assassination jolted lots of memories, some of them ordinary. “Stereo console with FM/AM radio,” shouted one ad in the 1963 edition of The Post.

The fallen political clout of New York is also eye-catching. Kennedy won the state’s 45 electoral votes in 1960 — an exorbitant tally next to the 29 we have now. New York also had 29 in the election of 1812.

So, yes, the Empire State is going backwards.

Tale of 2 sickies

Legendary ad man Jerry Della Femina wants to trade Bill de Blasio for Toronto Mayor Rob Ford. As Della Femina wrote in the newspaper he owns, his pitch would be: “Rob, if you like your crack pipe, you can keep your crack pipe.”

How best to employ Bratton

Bill Bratton is on Bill de Blasio’s short list to be the next police commissioner, but I suspect he won’t get the job. In fact, I hope he doesn’t.

Not that Bratton isn’t qualified. Rather, I think he’s better suited for another important post. He should be the deputy mayor for public safety and oversee all law-enforcement and security issues.

Bratton’s been the top cop in Boston, New York and Los Angeles, meaning he’s been around the track. He’s got a great record and there aren’t many commissioner challenges left for the 66-year-old Vietnam vet. As an elder statesman in the policing revolution of the last 20 years, it’s time for him to move into City Hall.

He would be more valuable there to de Blasio. The new mayor is alienated from the police, fire and anti-terror culture and will need a Sherpa to guide him through the challenges he’ll face. From analyzing terrorism threats to responding to major emergencies, crime and other police issues, Bratton has seen and done it all.

Having Bratton by his side also would let de Blasio pick a younger, proven leader from the NYPD. Two under consideration, Philip Banks III, chief of the department, and Rafael Pineiro, the first deputy commissioner, were groomed by Ray Kelly, and either would provide continuity as well as fresh eyes.

Mayor Bloomberg didn’t have a deputy mayor for public safety, but he did have Kelly. Because de Blasio is committed to driving out the most successful commissioner ever, he will need a bigger management structure to fill the holes. Bratton would make an ideal leader of that team.