President-elect Donald Trump is selecting radical MAGA loyalists for top national security positions, signaling his intention to upend the professionalism and independence of institutions that wield some of the federal government’s most awesome powers.

Political opponents, journalists and others could be victims. And President Joe Biden just gave him cover.

To be clear: Mr. Biden had an unquestionable legal right to pardon his son Hunter. But in so doing on Sunday, he maligned the Justice Department and invited Mr. Trump to draw equivalence between the Hunter Biden pardon and any future moves Mr. Trump might take against the impartial administration of justice.

He risks deepening many Americans’ suspicion that the justice system is two-tiered, justifying Mr. Trump’s drive to reshape it — or, because turnabout is fair play, to use it to benefit his own side.

Mr. Biden, of course, argues that pardoning his son strikes a blow for fairness in law enforcement. His statement on the pardon — in which he uses the words, “I believe in the justice system, but …” — claims that “no reasonable person” could “reach any other conclusion than Hunter was singled out only because he is my son.” Yet such considerations were apparently not so compelling when he pledged previously not to pardon Hunter. And his son clearly broke the law.

A federal jury of Hunter Biden’s peers found him guilty of three firearm-related felonies in Delaware. Hunter also pleaded guilty to tax evasion charges that carry a penalty of up to 17 years in prison. The gun charges, essentially that the younger Mr. Biden lied on a purchase application form when he denied using drugs, is particularly hard to ignore.

Such laws, however rarely enforced, are on the books to help keep firearms out of the hands of those who might pose a danger to themselves or others.

By implication, Mr. Biden casually impugns investigators at the IRS and the FBI, career prosecutors, Attorney General Merrick Garland and a federal judge in Delaware. Before Mr. Garland became attorney general, Mr. Biden himself chose to keep David C. Weiss as U.S. attorney for Delaware so as not to interfere with Mr. Weiss’s ongoing investigation of the president’s son.

In his statement, Mr. Biden complains that a plea deal fell apart in court last summer. In fact, the judge did her job by questioning its irregular structure — highly favorable to Hunter Biden — and the degree to which the defendant believed it would immunize him from future prosecution for unrelated crimes.

The president’s sweeping pardon covered any and all federal crimes his son might have committed over the past 10 years, including those that have not been charged, without going through the traditional Justice Department process.

This covers potential illegal behavior by Hunter Biden going back to 2014, six years before Mr. Biden became president.

Mr. Biden rushed out this pardon on Sunday night to short-circuit the sentencing process in both cases in the coming weeks.

This averts a meaningful part of the accountability process, in which judges would have decided whether Hunter Biden deserved to serve time in prison. Justice Department guidelines say a pardon shouldn’t be issued until five years after a sentence is served. That was the case when Bill Clinton pardoned Roger Clinton after the president’s brother had served time for cocaine trafficking.

Yes, Mr. Trump egregiously misused the pardon power during his first term, granting clemency to Stephen K. Bannon, Roger Stone, Michael Flynn and Charles Kushner, his son-in-law’s father, whom he just tapped to be ambassador to France.

These sent the message that Mr. Trump will get his cronies off the hook, at the risk of encouraging further unlawful behavior.

Yet, no matter the distinctions that one can draw between these cases and Hunter Biden’s, the president — and the Democrats — are the ones trying to defend the system; they damage their worthy cause if they are seen to be exploiting it for their own gain.

Any Democrat who refuses this week to condemn Mr. Biden’s pardon will have less credibility to criticize Mr. Trump, his meddling at the Justice Department and his choices for key positions in that agency.

No one should be surprised if Mr. Trump invokes the Hunter Biden pardon to justify clemency for many more of his allies, potentially including Jan. 6 insurrectionists.

With this one intemperate, selfish act, the president has undermined, in hindsight, the lofty rationales he offered for seeking the presidency four years ago and indelibly marred the final chapter of his political career.