WASHINGTON — Tucked between St. Patrick’s Day greetings and repeat criticism of a rerun of “Saturday Night Live,” President Trump demonstrated that not even death provides a respite from his wrath on Twitter.
In posts on Saturday and Sunday, Mr. Trump renewed his criticism of Senator John McCain, the Arizona Republican who died in August from complications from a virulent form of brain cancer.
The president attacked Mr. McCain over his role in the Justice Department investigation into Russian efforts to influence the 2016 presidential election. He then added that Mr. McCain “had far worse ‘stains’ ” on his record, including the senator’s decisive vote against repealing the Affordable Care Act.
“Spreading the fake and totally discredited Dossier ‘is unfortunately a very dark stain against John McCain,’” he tweeted on Saturday, quoting comments in a Fox News interview by the former independent counsel Ken Starr about the so-called Steele Dossier, which outlined a range of often salacious but unproven misdeeds by Mr. Trump and his associates.
“So it was indeed (just proven in court papers) ‘last in his class’ (Annapolis) John McCain that sent the Fake Dossier to the FBI and Media hoping to have it printed BEFORE the Election,” he wrote on Sunday. “He & the Dems, working together, failed (as usual). Even the Fake News refused this garbage!”
In fact, Mr. McCain provided a copy of the dossier to the F.B.I. after Election Day. But supporters of Mr. Trump have seized on the dossier’s uncorroborated accusations and political roots in the campaign as a way to try to discredit the special counsel’s Russia inquiry.
The comments exemplified Mr. Trump’s model for presidential communication, both in form and tone, exploiting the power and urgency of social media, often with harsh and bitterly personal attacks. But they also sparked swift condemnation, showing that the president abandons conventional boundaries of civility like not speaking ill of the dead at his peril.
“There’s no low with him,” John Weaver, who was a political adviser to Mr. McCain, said in an interview. “There’s no bottom.”
Mr. Trump and Mr. McCain had a long history of enmity, one that lasted even through the senator’s death. Mr. McCain made it clear that Mr. Trump was not welcome at his memorial service in Washington, even as both President Barack Obama, who defeated Mr. McCain in the 2008 presidential race, and President George W. Bush, who defeated him in the Republican primaries in 2000, delivered eulogies.
And over the weekend, the tensions resurfaced, as McCain supporters denounced the president’s tweets — and, in many cases, the president himself.
Mr. Weaver criticized Mr. Trump’s avoidance of service in Vietnam, where Mr. McCain was held captive as a prisoner of war, his refusal to release his own grades while criticizing Mr. McCain’s academic performance at the United States Naval Academy, and the president’s desire to terminate the Affordable Care Act.
“These are the things he wanted to attack John McCain on? Seriously?” Mr. Weaver said.
“I am waiting for Republican members of the Senate who served with the senator for years and allowed him to be the point of the spear on so many issues,” he said. “Where are they?”
Senator Lindsey Graham, Republican of South Carolina and one of Mr. McCain’s closest friends, chose to praise his friend rather than criticize the president.
“As to @SenJohnMcCain and his devotion to his country: He stepped forward to risk his life for his country, served honorably under difficult circumstances, and was one of the most consequential senators in the history of the body,” he said on Twitter. “Nothing about his service will ever be changed or diminished.”
Mike Murphy, another McCain political adviser, displayed no such reluctance to chastise the president: “McCain was a hero,” he said. “Trump is a whimpering coward. He was afraid to go to Vietnam 47 years ago and is afraid to face the legal consequences of his actions today.”
“He just has no empathy,” Mr. Murphy said. “He’s only concerned with himself.”
Mark Salter, one of Mr. McCain’s closest advisers and co-author of several books with him, was even more biting.
“Here is what will never change,” Mr. Salter said in a tweet. “John McCain will always be a better man than you in every way we measure a man’s character. You’ll never beat him.”
The White House did not respond to a request for comment about Mr Trump’s remarks.
Still, Mr. Trump insisted on using Mr. McCain as a posthumous whipping post, even taking a dig at Mr. McCain’s academic record, calling him “last in his class.” Mr. McCain often mocked his own performance in the classroom as a midshipman, and never shied from noting that he graduated fifth from the bottom.
The president had no public events on his schedule this weekend, but he kept up a barrage of tweets. He called for fealty to the Fox News personalities Jeanine Pirro, who was suspended by the network after questioning a Muslim lawmaker’s loyalty to the United States, and Tucker Carlson, who has come under criticism for his remarks on a shock-jock radio program about a decade ago. Mr. Trump also again threatened to use the federal government to crack down on programs that make fun of him, singling out “Saturday Night Live.”
He did participate in one unscheduled event, taking a short car ride across Pennsylvania Avenue on Sunday to attend services at St. John’s Episcopal Church, a rarity for Mr. Trump.
The second reading, according to the program, was from Philippians, which begins “join together in following my example, brothers and sisters, and just as you have us as a model, keep your eyes on those who live as we do.”