As Robert S. Mueller III, the special counsel, has investigated his actions for more than a year, the president has waged a relentless campaign to diminish the Justice Department and the F.B.I. in the eyes of the public. After Michael D. Cohen, his longtime personal lawyer, pleaded guilty to campaign finance violations that he said had been directed by Mr. Trump, the president falsely claimed that the violations were not even a crime. And he has criticized federal courts as they have blocked much of his agenda, including his efforts to wield executive authority on immigration, voting and the environment.

George T. Conway III, a conservative Washington lawyer who is often critical of the president (and who is the husband of Kellyanne Conway, the president’s counselor), tweeted on Friday that “what everyone should want, and the country needs, is a ‘President’ capable of comprehending what it means to ‘take Care that the Laws be faithfully executed.’ Art. II, § 3.”

But Mr. Conway also offered a more hopeful observation, one that was echoed this past week by several constitutional and legal scholars: Many of the country’s law enforcement institutions seem to be standing up to Mr. Trump’s continued abuse — at least for now. As they always have, they are pursuing hundreds of cases across the country, even as the president is fixated on only one of them.

Asked on Twitter how the American government might react if a foreign leader showed the same disrespect for the rule of law, Mr. Conway said that “they might perceive that the system was so strong, its checks and balances so robust, that the ‘president’ is reduced to lamely tweeting insults at his attorney general, with no effect other than to continue to erode his own moral authority.”

The strength of the system was underscored on Tuesday, moments after Mr. Cohen pleaded guilty. Outside a courtroom in New York, Robert S. Khuzami, the deputy United States attorney, delivered a message that might have been directed squarely at the person in the Oval Office.

“That message is that the rule of law applies,” Mr. Khuzami said, standing in front of a phalanx of F.B.I. agents and federal prosecutors.

Paula Duncan, a firm supporter of Mr. Trump who served on the jury that convicted Mr. Manafort, made the same point in an interview on Saturday. Although she believes that Mr. Manafort was targeted because Mr. Mueller’s team hopes he is a steppingstone to Mr. Trump, she said, he was convicted because of “overwhelming” evidence.