IN AUGUST 2012, Dinesh D’Souza, a conservative author and polemicist, persuaded two people to make illegal campaign contributions to the U.S. Senate bid of New York Republican Wendy Long. This was no nickel-and-dime operation: Mr. D’Souza reimbursed two “straw donors” $10,000 each for making donations by themselves and their spouses. It was illegal because Mr. D’Souza had already reached the federal limit with his own contribution.

On May 20, 2014, Mr. D’Souza pleaded guilty in federal court to violating the federal election campaign law, and, according to the announcement by then-U.S. Attorney Preet Bharara, “admitted that he knew that what he was doing was wrong and something the law forbids.” A federal judge earlier dismissed Mr. D’Souza’s claim of selective prosecution, ruling there was no evidence of it. He was sentenced to five years probation, and a $30,000 fine.

On Thursday, President Trump pardoned Mr. D’Souza, claiming he “was very unfairly treated.” Mr. Trump has constitutional power to do this, and he is hardly the first president to grant clemency to an unsavory figure. What is offensive here is not the pardon power, but the use of it. Mr. Trump rewarded a man who consciously and brazenly violated the rules of the political system. In so doing he displayed open disdain for the courts, prosecutors and judges who identified Mr. D’Souza’s misdeeds and attempted to hold him to account.

The pardon is yet another worrisome indication of Mr. Trump’s disrespect for the U.S. justice system. He has waged an intemperate and incessant campaign against the special counsel’s continuing investigation of his 2016 campaign. The pardon is a signal — indeed, a warning — that he can alleviate or overturn any punishment meted out as a result of the Russia probe. Mr. Trump also bypassed the rigorous process and standards, overseen by the U.S. pardon attorney, that thousands of others submit to in pursuit of clemency. This is Mr. Trump’s prerogative, but it suggests the pardon was arbitrary, political and unjustified.

Mr. Trump suggested he wants to pardon former Illinois Democratic governor Rod R. Blagojevich, who has served six years of a 14-year sentence for corruption, and was once overheard on a court-authorized FBI wiretap boasting of his plans to sell a U.S. Senate seat to the highest bidder. Before going to jail, however, the flamboyant politician made an appearance on Mr. Trump’s television show, “Celebrity Apprentice.” Mr. Trump is also talking about a pardon for television celebrity Martha Stewart, who spent five months in prison for lying to investigators in a stock case, and briefly headed a spinoff of Mr. Trump’s program. The logic behind such actions is authoritarian; pardons as the product of presidential whims and personal favors.

What is at stake here is not legality, but democratic values. Mr. Trump conducts himself as chieftain of his own clan, not the protector of the rule of law for the nation as a whole.

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