The Justice Department’s internal watchdog has been investigating why ex-FBI deputy director Andrew McCabe apparently sat on his hands for about three weeks after Hillary Clinton’s emails were found on Anthony Weiner’s laptop, a new report said Tuesday.

Inspector General Michael Horowitz wants to know why some top FBI officials appeared less than enthusiastic about probing the emails, which were sent by top Clinton aide Huma Abedin, Weiner’s long-suffering wife, The Washington Post reported.

McCabe waited until late October — just weeks before the election and roughly three weeks after they were discovered — to begin scrutinizing the messages, some of which were classified.

Horowitz is trying to figure out whether McCabe or anyone else at the bureau wanted to delay action on the emails until after the election — but has not come to any conclusions, the paper reported.

He also wants to know who knew about Clinton’s emails on Weiner’s laptop — which were discovered in late September 2016 — and when they learned about them.

Then-FBI director James Comey announced in late October that the bureau was reopening its probe of Clinton’s use of a private email server as secretary of state in light of the Weiner discovery.

Clinton backers slammed Comey at the time, saying the 11th-hour announcement hurt Clinton and helped Trump.

Days later, Comey again shut down the probe and said the emails added nothing new to the case.

McCabe’s defenders told the paper that there was nothing suspicious going on and that FBI brass were being cautious about evaluating the emails so close to the election.

But pressure on the brass was mounting within the bureau to move on the emails after it was disclosed that McCabe’s wife, Jill, had received hundreds of thousands of dollars for her Virginia state Senate bid from a PAC connected to then-Gov. Terry McAuliffe, a longtime Clinton crony.

Jill McCabe lost that race — but the revelation enraged Trump, who took to Twitter to attack the couple, saying the donation proved McCabe was biased against him.

“How can FBI Deputy Director Andrew McCabe, the man in charge, along with leakin’ James Comey, of the Phony Hillary Clinton investigation (including her 33,000 illegally deleted emails) be given $700,000 for wife’s campaign by Clinton Puppets during investigation?” he wrote on Dec. 23.

FBI Director Chris Wray, meanwhile, told his troops that McCabe abruptly resigned over concerns about the IG’s report — not because of repeated attacks from Trump.

Wray sent a message to the bureau’s staffers hours after McCabe announced that he was stepping down — though he will remain on the payroll using accrued time off until March, when his pension benefits max out.

Wray said he had seen parts of the IG’s report on how the FBI handled the investigation into Hillary Clinton’s use of a private e-mail server as secretary of state, NBC News reported.

“It would be inappropriate for me to comment on specific aspects of the IG’s review right now,” Wray said in the message, denying that pressure from the administration and its Congressional allies played a role in the departure.

“But I can assure you that I remain staunchly committed to doing this job, in every respect, ‘by the book.’ I will not be swayed by political or other pressure in my decision making.”

Trump thought McCabe, a career G-man who once worked in the New York office, was too friendly with Comey.

The president flew into a rage when he saw on TV that Comey had taken a government plane home from Los Angeles after Trump fired him over the ongoing probe into Russian meddling in the US election and possible collusion with Team Trump.

The commander-in-chief phoned McCabe and demanded to know who had approved it.

McCabe replied that he didn’t authorize the flight — but would have if asked.

The president then told McCabe that he should call his wife and ask her how it feels to be a loser.

“OK, sir,” McCabe replied, and Trump hung up on him.

Jill McCabe is a mother of two and a highly regarded pediatric emergency physician and hospital administrator in the capital area.