Chief of staff John Kelly digs himself in deeper every time he opens his mouth.

Chief of staff John Kelly was supposed to be a moderating influence over Trump, and even the “adult” in the room.

But similarly to his boss, Kelly doesn’t seem to know when to stop talking, even when his words just keep digging himself deeper and deeper into a public relations hole.

Instead of following in Trump’s reckless footsteps, Kelly might want to heed the advice of his friend and one-time colleague, former Homeland Security chief under President Obama, Jeh Johnson.

That advice? Essentially, “stop talking.”

As reports emerged that now-former White House aide Rob Porter had allegedly verbally and physically abused three women — two ex-wives and an ex-girlfriend — Kelly’s handling of the situation was no better than Trump’s.

Indeed, the White House has gone all in on defending Porter, with Kelly leading the way alongside Trump.

The day before Porter’s resignation in disgrace, Kelly was out front praising him as “a man of true integrity and honor” about whom he “can’t say enough good things.” He called Porter a “friend, a confidante and a trusted professional,” and urged him to “stay and fight” — an interesting choice of words.

After Porter resigned, Kelly feigned shock at the new allegations. While he insisted that he believes there’s “no place for domestic violence in our society,” he also made sure to note that he “[stands] by my previous comments of the Rob Porter that I have come to know since becoming Chief of Staff, and believe every individual deserves the right to defend their reputation.”

But all the claims of shock and dismay ring hollow in light of the fact that Kelly knew full well about Porter’s record when Porter was brought on board.

When asked by CNN’s Jake Tapper about Kelly’s handling of the Porter scandal, Johnson made clear that while Kelly is a respected former colleague as well as a friend of his, his behavior of late needs to change.

“My friendly advice to him is: Less press [and] fewer public statements,” Johnson declared.

Johnson referenced a quote from Leon Panetta — secretary of defense under Obama and chief of staff to President Bill Clinton — who noted that “the chief of staff is someone who should not be the issue.”

“I encourage John to hunker down and do his job,” Johnson continued. “Fewer public statements.”

Whether Kelly will choose to heed the wisdom of his friend and colleague, or instead continue to wallow in the muck alongside Trump, remains to be seen.

But if he wants to still be seen as that ostensible “adult” in the White House, a good place to start would be to refrain from sinking down to Trump’s childish level.