President Johnson? (Richard Shotwell/Invision via AP)

It started off as a joke, then it became more serious. Now Dwayne “the Rock” Johnson says running for president in 2020 is “a real possibility.”

The pro wrestler and Hollywood mogul made his latest quips to GQ magazine, which published a highly entertaining cover story on the star Wednesday.

Johnson said it was about a year ago, around the time The Post’s Alyssa Rosenberg published an essay explaining why Johnson could be a viable candidate, that the actor began thinking about running for office more seriously.

“There was a real sense of earnestness, which made me go home and think, ‘Let me really rethink my answer and make sure I am giving an answer that is truthful and also respectful,’ ” he told GQ’s Caity Weaver.

“I didn’t want to be flippant,” he added about what his platform might be, such as giving joke responses like “We’ll have three days off for a weekend!” or “No taxes!”

Weaver writes: “So, after all that consideration, Johnson doesn’t hesitate when I ask him whether he honestly might one day give up his life as the highest-paid movie star on earth — which is unquestionably easier, more fun, and more lucrative than being president of the United States — in order to run for office. ‘I think that it’s a real possibility,’ he says solemnly.”

Johnson’s newfound seriousness on the subject stands in contrast to his brand of humor with which he previously approached the subject. He once tweeted that if he ran for office and won that the White House better have a spot for his pickup truck.

Johnson also poked fun at his presence in the Oval Office on “SNL” in 2013 and again in 2015, when he played a hulking version of former president Barack Obama.

Johnson, however, suggested to Weaver that he’d be much more level-headed than “The Rock Obama,” emphasizing that being able to listen to those you disagree with and compromise as two features he’d bring to the job.

“When there’s a disagreement, and you have a large group of people that you’re in a disagreement with — for example, the media — I feel like it informs me that I could be better,” he said. “We all have issues, and we all gotta work our [crap] out.”

He added, “[Disagreement] informs us. The responsibility as president — I [would] take responsibility for everyone. Especially when you disagree with me. If there’s a large number of people disagreeing, there might be something I’m not seeing, so let me see it. Let me understand it.”

Johnson didn’t reveal any specific platforms he’d run on, nor did he say for which party he might seek the nomination. A registered independent, Johnson has been affiliated with the Republican and Democratic parties, having attended both national conventions in 2000 to encourage people to vote. As for whom he voted last year, however, Johnson kept that a secret, although, again, both parties sought his public endorsement, he told GQ.

“I feel like I’m in a position now where my word carries a lot of weight and influence, which of course is why they want the endorsement,” he said. “But I also have a tremendous amount of respect for the process and felt like if I did share my political views publicly, a few things would happen … I felt like it would either (a) make people unhappy with the thought of whatever my political view was. And, also, it might sway an opinion, which I didn’t want to do.”

Since President Trump was inaugurated in January, however, Johnson hasn’t remained totally silent. He made clear he had some philosophical differences with Trump’s policies on immigration when he distanced himself from Under Armour chief executive Kevin Plank in February after Plank declared Trump was an “asset” to the country for his “pro-business” and hard line immigration stances.

Johnson reiterated his difference of opinion with Trump when Weaver asked him about his views of the president’s latest executive order on immigration, which put a temporary ban on entry to the United States by people from six majority-Muslim countries.

“I completely disagree with it,” he told GQ. “I believe in our national security to the core, but I don’t believe in a ‘ban’ that bans immigrants. I believe in inclusion. Our country was built on that, and it continues to be made strong by that.”

Sounding very much like a politician already, Johnson added it’s important not to make a “snap judgment” when it comes to national-security decisions. It appears that’s how he might feel about running for office, too.