As the White House was gearing up to sell ObamaCare to the American people last summer, Valerie Jarrett, the president’s pointwoman on a host of issues, phoned Oprah Winfrey.

She invited the Queen of All Media to join celebrities, including Amy Poehler, Jennifer Hudson and Alicia Keys, to meet with President Obama and discuss how they could generate publicity for his health-care law.

Oprah refused.

“All of Oprah’s top people thought she would go, because when the president invites you to the White House, most people automatically say yes,” said one of Oprah’s closest advisers. “But Oprah said she didn’t have the time or inclination to go. It wasn’t like she had to think it over. It was an immediate, flat-out, unequivocal no.”

Instead, Oprah sent a low-level rep from one of her talent agencies, which was regarded as a insult. Obama had been counting on Oprah’s immense persuasive powers to help enroll millions in ObamaCare. But as the rollout turned into a disaster, Oprah didn’t lift a finger to help.

The story of why Oprah has changed her tune and gone AWOL on ObamaCare goes well beyond mere gossip. It speaks volumes about the convergence of celebrity and politics under Obama and about a president who thinks nothing of using and then discarding his most loyal supporters.

Everyone remembers that Oprah went all out for Obama during the 2008 presidential election. What was not reported was that, in return, Oprah was promised unique access to the White House if Obama won. She’d get regular briefings on initiatives and a heads-up on programs to give her material for her fledgling cable network, OWN.

“Oprah intended to make her unique White House access a part of her new network,” a source close to Oprah told me. “There were big plans, and a team was put together to come up with proposals that would have been mutually beneficial.

“But none of that ever happened. Oprah sent notes and a rep to talk to Valerie Jarrett, but nothing came of it. It slowly dawned on Oprah that the Obamas had absolutely no intention of keeping their word and bringing her into their confidence.”

Oprah did not campaign for Obama in the 2012 race, and she has been absent from his battles on gun control, immigration reform and the environment. She claims she is too busy to get involved in politics, even though she hosted a fund-raiser for Newark Mayor Cory Booker, who won a US Senate seat last week.

Oprah’s friends publicly dismiss the idea that she had a falling out with Obama. They note that she phoned Michelle Obama right after the 2012 election to congratulate her. They say Michelle invited her to have dinner with the first family. But the dinner never took place, and Oprah continues to be frozen out.

“Oprah was hoping there would be a genuine change in the atmospherics,” one of her friends told me. “But there hasn’t been. Clearly, she is being rebuffed at the level of Michelle and Valerie. And, just as obviously, President Obama hasn’t interfered on Oprah’s behalf.”

During Obama’s first term, I argued in my book “The Amateur” that Michelle was jealous of Oprah, furious that he was seeking her advice.

“For her part, Oprah doesn’t like being with Michelle, because the first lady is constantly one-upping the president and anybody else around her,” said an Oprah adviser.

“Oprah has struck back by banning the Obamas from her O, The Oprah Magazine . . . It probably hurts Oprah more than Obama, who, if he had his head screwed on straight, would have flown to California and begged Oprah to help him save ObamaCare.

“But Obama hasn’t budged, and neither has Oprah. She’s hurt and angry, and I seriously doubt that Oprah will ever make up with the Obamas. She knows how to hold a grudge.”

Edward Klein is the author of the New York Times No. 1 best seller “The Amateur,” available in paperback.