City Council Speaker Corey Johnson is not letting his new nickname “de-facto mayor” go to his head, but he took another shot at Hizzoner for being missing in action during last weekend’s blackout.

“They say that 90 percent of life is showing up. Well, 100 percent of being an elected official is showing up,” he told The Post during a wide-ranging interview Thursday.

The 37-year-old Democrat, who many see as the leading contender to succeed de Blasio in the 2021 race, suggested the mayor should have immediately returned from stumping in Iowa.

“I came back,” he said. “I wasn’t in the city. I was on Long Island and I came back right away.”

The real-time leadership, which included frequent and detailed updates on Con Ed restoration work and subway closures on Twitter, had commenters calling “CoJo” the city’s real mayor.

“It’s flattering in some ways, but I am not sure it totally comports with reality,” he said.

Political donors seem to think so. Johnson has raised $379,728 while exploring a possible mayoral run in 2021, bringing his war chest to $431,549, according to city filings. That puts him behind top fundraiser city Comptroller Scott Stringer, who has $2,587,656 in his coffers. But Johnson’s aides note he is taking no money from developers, and capping contributions at $250.

“The city has been so good to me,” he said. “It would be the honor of my life to be able to lead the city.”

Johnson came from Massachusetts to the Big Apple at age 19 with no college degree and few connections. After working on his local community board for years, he won a Council seat to rep Chelsea, Greenwich Village and Midtown West in 2013.

If he runs for City Hall and wins, he could face two of the biggest personalities in politics — President Trump and Gov. Cuomo.

Johnson dismissed the possibility of working with Trump, whom he called a “racist.”

“It’s almost impossible to work with someone who has continually tried to undercut the city of New York and has done things to hurt us economically,” Johnson said of the commander-in-chief.

While de Blasio has feuded with Gov. Cuomo since nearly the start of his administration, Johnson sang the governor’s praises.

“Gov. Cuomo has had some very significant wins that have benefitted New Yorkers,” the speaker said. “You have to be able to have a good relationship … with the governor.”

Recent weeks have seen a war of words between democratic socialist Rep. Alexandria Ocasio-Cortez (D-Queens/Bronx) and House Speaker Nancy Pelosi, but Johnson said the debate is “good for the party.”

He defended AOC’s remarks last month comparing migrant detention centers at the US southern border to “concentration camps.”

“I don’t think it’s inappropriate to describe things in a way that show racism, that show childhood separation and so I am not offended by the congresswoman making that comment.” He didn’t answer when asked if he would use the term “concentration camp.”

Asked if he adheres to democratic socialism — the movement championing big government and taking a skeptical view of capitalism — he said, “I would describe myself as a left-of-center progressive Democrat.”

He partially disagrees with one of the latest democrat socialists to gain prominence — Tiffany Cabán, who is locked in a vote recount battle for Queens district attorney.

While Cabán campaigned on a promise to stop prosecuting both sex workers and johns and pimps, Johnson said the latter two groups should not be spared arrest.

“I don’t support the full [decriminalization] mode,” he said, but agrees with Caban on steering sex workers to health care and other programs recently passed by the Council.

In May, Johnson proposed sweeping criminal-justice reforms aimed at sending offenders to social services programs instead of jail. If elected mayor, he would continue the recent trend of shunning broken-windows policing.

“Broken windows policing hasn’t worked. The city is still safe, even with fewer arrests,” he said, pointing to the 50-percent drop in city jail admissions since 2010. “You can still do some quality-of-life policing as a deterrent — not in arresting individuals unless it is of a certain crime — and the city will still continue to function.”

Defenders of broken window policing note subway and bus fare evasion is up, with the MTA losing an estimated $215 million last year. And while murders reached an all-time low last month, shootings for the year to date spiked 7.1 percent. And many credit the Giuliani and Bloomberg administrations’ focus on quality-of-life crime with the start of the decades long decline in more serious crime in NYC.

Looking to the Democratic presidential primary, Johnson said, “I sort of feel like a lot of Democrats, which is slightly fickle.”

Undecided on a candidate, CoJo said he has met with Sens. Kamala Harris and Elizabeth Warren along with South Bend, Ind., Mayor Pete Buttigieg, who, like Johnson, is openly gay. He has met three times with Buttigieg and has even met his husband.

“To have one of the top-tier candidates be a 37-year-old openly gay former military man … shows how much progress there has been,” said Johnson, who is HIV-positive and single.

Conspicuously absent from Johnson’s discussion of the Democratic presidential primary were the two New York hopefuls, Sen. Kirsten Gillibrand and de Blasio.

The speaker said, “I look forward to the field getting whittled down.”