The president flew into Wilmington, Del., on Sunday night, where his 54-year-old son’s felony gun trial begins Monday, and will spend the whole day there with no official duties.

Joe Biden’s looming presence in the strange small city leaves nobody in any doubt of the message he is sending to Delaware special counsel David Weiss, the prosecutors, the judge, and the jury pool being chosen Monday: You mess with my son, you mess with me.

It’s all very subtle, in a flagrant way, much like Joe’s impromptu visit to Hallie Biden, the widow of Beau and former lover of Hunter, just nine days before his son’s trial, at which she is the star witness for the prosecution.

It was Hallie who threw Hunter’s new handgun in a trash can in October 2018 out of concern for his drug-addled mental state, creating a ticking legal time bomb that would propel him into court six years later.

It was Hallie who found drugs and drug paraphernalia in his truck. Hallie, 50, even shared his crack addiction for a time, amid multiple drug rehab efforts.

‘Word as a Biden’?

In a trial based on the allegation that Hunter lied on the gun shop’s federal background form on Oct. 12, 2018, when he checked “No” on the question, “Are you an unlawful user of, or addicted to” various narcotic drugs, Hallie’s understanding of his drug use will be key. Hunter’s defense is that the day he bought the gun was a rare day of sobriety in a period during which he admitted in his memoir, “Beautiful Things,” “I was smoking crack every 15 minutes.”

The potential for witness tampering in Joe’s late-night visit to Hallie was obvious, and must have caused conniptions for the prosecutors, Weiss’ towering deputies Leo Wise and Derek Hines.

Yet again we are commanded to take Joe’s “word as a Biden” that nothing untoward went on.

Joe’s ever-present suite of family tragedies was offered to explain the visit, in this case the upcoming anniversary of Beau Biden’s death, not that previous anniversaries had occasioned a high-profile, late-night presidential visit.

Nor did Joe and Hallie need to discuss the trial in their 15-minute private meeting.

The president’s mere unscheduled presence said it all.

As part of this wise-guy messaging, conspicuous Hunter sightings alongside his father have accelerated in the last two weeks.

There was Hunter at the White House, wagging his finger at staff, or attending an event in the Rose Garden.

Here he was, getting on and off Marine One and Air Force One with his father, flying for long weekends from Washington to Wilmington to Rehoboth Beach, Del., and back again, hopping in and out of the presidential motorcade, his own Secret Service detail in tow.

On Saturday morning came a new iteration: Hunter riding a bike with Dad in Rehoboth, sticking close behind as they passed the waiting media.

Perhaps the most flagrant of all was the May 23 state dinner for the president of Kenya where, yet again, the indicted first son rubbed shoulders with Attorney General Merrick Garland.

A dozen Biden family members and hangers-on also attended, including Hunter’s three daughters and niece plus boyfriends and a husband.

It’s the second state dinner Garland has attended with Hunter at a crucial moment in the first son’s legal odyssey.

Before IRS whistleblowers revealed the corrupt Justice Department and CIA obstruction of the five-year criminal tax fraud investigation of Hunter last year, he sealed a sweetheart plea deal with then-plain old Delaware US Attorney Weiss, and a few days later was swanning around triumphantly at the state dinner for the Indian prime minister. Garland was there in his penguin suit, warily trying to keep a discreet distance between them.