The 2020 presidential race is about to be hit by an O-bomb.

Former President Barack Obama is champing at the bit to jump into the campaign fray on behalf of his vice president Joe Biden, and is sharpening his knives for President Trump, his aides and advisors told The Post.

“He is very eager to do this,” said a former senior Obama official who remains in regular touch with his old boss. “I certainly expect President Obama to be very active.”

Though Obama has followed the tradition of past presidents in avoiding day-to-day criticism of his successor, those familiar with his thinking say he has been particularly roused in recent months by Trump’s performance handling COVID-19.

“The coronavirus disaster and the [federal] government’s inability to lead on it is searing in his brain … more than anything else Trump has done,” said a second insider. “Obama is generally heartbroken by the Donald Trump presidency.”

Obama insiders said the ex-president would be careful to let Team Biden call the shots and make the final decisions about when and how to deploy him.

Obama has spoken up against the Trump administration from time to time — often while stumping for candidates during the 2018 midterms — but has almost religiously avoided attacking Trump by name.

On Tuesday, Obama officially gave his blessing to Biden in a Twitter video statement.

“The kind of leadership that’s guided by knowledge and experience, honesty and humility, empathy and grace — that kind of leadership doesn’t just belong in our state capitols and mayors offices. It belongs in the White House,” he said.

Up until that moment, Obama had famously sat on the sidelines during the 2020 Democratic primaries, leaving his former veep to weather brutal attacks. The cold shoulder raised eyebrows throughout the race, particularly after reports said Obama had discouraged Biden from seeking the nomination.

“You don’t have to do this, Joe, you really don’t,” Obama reportedly told Biden when he was considering a run. The 44th president also leaned on Biden political advisers Anita Dunn and Kate Bedingfield to intercede, warning that Biden could “embarrass himself” or “damage his legacy,” the Times reported. In January 2019 — before Biden entered the race — Obama said the party needed “new blood” to beat Trump.

Any lingering bad feelings, however, have been smoothed over, reps for both men say.

“Their warmth was visible every week for eight years,” Brian Mosteller, Obama’s longtime director of Oval Office operations told The Post, describing regular lunches between the men and weekend outings to basketball games. “There is a genuine mutual respect.”

Another insider added: “[Biden] gets over things quickly. He doesn’t take stuff personally. He’s been around the block.”

It’s still unclear exactly what the plan for Obama will be on the campaign trail, and how the coronavirus might limit his ability to stump. But the overall favorables are tantalizing.

“While COVID-19 has put an end to in-person events, President Obama can still be deployed in a number of ways to help Vice President Biden, including unlocking his massive fundraising network, continuing to be visible in online videos that get big audiences, serving as a high-profile surrogate in a wide range of media and helping unify the party to face Trump,” Democratic strategist Eric Koch told The Post.